diff --git a/ChangeLog b/ChangeLog
index b4db031db4..5739517978 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -41,7 +41,6 @@ API Changes
      mbedtls_ctr_drbg_update() -> mbedtls_ctr_drbg_update_ret()
      mbedtls_hmac_drbg_update() -> mbedtls_hmac_drbg_update_ret()
    * Extend ECDH interface to enable alternative implementations.
-<<<<<<< HEAD
    * Deprecate the ARIA error MBEDTLS_ERR_ARIA_INVALID_KEY_LENGTH
      in favour of a new generic error MBEDTLS_ERR_ARIA_BAD_INPUT_DATA.
    * Deprecate the CAMELLIA error MBEDTLS_ERR_CAMELLIA_INVALID_KEY_LENGTH
@@ -56,6 +55,8 @@ API Changes
      module.
    * Add validation checks for input parameters to functions in the SHA-512
      module.
+   * Add validation checks for input parameters to functions in the Cipher
+     module.
 
 New deprecations
    * Deprecate mbedtls_ctr_drbg_update and mbedtls_hmac_drbg_update
diff --git a/include/mbedtls/cipher.h b/include/mbedtls/cipher.h
index 58a5d63ddc..922b6c32c6 100644
--- a/include/mbedtls/cipher.h
+++ b/include/mbedtls/cipher.h
@@ -36,6 +36,7 @@
 #endif
 
 #include <stddef.h>
+#include "mbedtls/platform_util.h"
 
 #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
 #define MBEDTLS_CIPHER_MODE_AEAD
@@ -336,11 +337,12 @@ const int *mbedtls_cipher_list( void );
  * \brief               This function retrieves the cipher-information
  *                      structure associated with the given cipher name.
  *
- * \param cipher_name   Name of the cipher to search for.
+ * \param cipher_name   Name of the cipher to search for. This must not be
+ *                      \c NULL.
  *
  * \return              The cipher information structure associated with the
  *                      given \p cipher_name.
- * \return              NULL if the associated cipher information is not found.
+ * \return              \c NULL if the associated cipher information is not found.
  */
 const mbedtls_cipher_info_t *mbedtls_cipher_info_from_string( const char *cipher_name );
 
@@ -352,7 +354,7 @@ const mbedtls_cipher_info_t *mbedtls_cipher_info_from_string( const char *cipher
  *
  * \return              The cipher information structure associated with the
  *                      given \p cipher_type.
- * \return              NULL if the associated cipher information is not found.
+ * \return              \c NULL if the associated cipher information is not found.
  */
 const mbedtls_cipher_info_t *mbedtls_cipher_info_from_type( const mbedtls_cipher_type_t cipher_type );
 
@@ -368,7 +370,7 @@ const mbedtls_cipher_info_t *mbedtls_cipher_info_from_type( const mbedtls_cipher
  *
  * \return              The cipher information structure associated with the
  *                      given \p cipher_id.
- * \return              NULL if the associated cipher information is not found.
+ * \return              \c NULL if the associated cipher information is not found.
  */
 const mbedtls_cipher_info_t *mbedtls_cipher_info_from_values( const mbedtls_cipher_id_t cipher_id,
                                               int key_bitlen,
@@ -376,6 +378,8 @@ const mbedtls_cipher_info_t *mbedtls_cipher_info_from_values( const mbedtls_ciph
 
 /**
  * \brief               This function initializes a \p cipher_context as NONE.
+ *
+ * \param ctx           The context to be initialized. This must not be \c NULL.
  */
 void mbedtls_cipher_init( mbedtls_cipher_context_t *ctx );
 
@@ -383,6 +387,10 @@ void mbedtls_cipher_init( mbedtls_cipher_context_t *ctx );
  * \brief               This function frees and clears the cipher-specific
  *                      context of \p ctx. Freeing \p ctx itself remains the
  *                      responsibility of the caller.
+ *
+ * \param ctx           The context to be freed. If this is \c NULL, the
+ *                      function has no effect, otherwise this must point to an
+ *                      initialized context.
  */
 void mbedtls_cipher_free( mbedtls_cipher_context_t *ctx );
 
@@ -392,7 +400,7 @@ void mbedtls_cipher_free( mbedtls_cipher_context_t *ctx );
  *                      structure with the appropriate values. It also clears
  *                      the structure.
  *
- * \param ctx           The context to initialize. May not be NULL.
+ * \param ctx           The context to initialize. This must be initialized.
  * \param cipher_info   The cipher to use.
  *
  * \return              \c 0 on success.
@@ -405,19 +413,22 @@ void mbedtls_cipher_free( mbedtls_cipher_context_t *ctx );
  * In future versions, the caller will be required to call
  * mbedtls_cipher_init() on the structure first.
  */
-int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx, const mbedtls_cipher_info_t *cipher_info );
+int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx,
+                          const mbedtls_cipher_info_t *cipher_info );
 
 /**
  * \brief        This function returns the block size of the given cipher.
  *
- * \param ctx    The context of the cipher. Must be initialized.
+ * \param ctx    The context of the cipher. This must be initialized.
  *
- * \return       The size of the blocks of the cipher.
- * \return       0 if \p ctx has not been initialized.
+ * \return       The block size of the underlying cipher.
+ * \return       \c 0 if \p ctx has not been initialized.
  */
-static inline unsigned int mbedtls_cipher_get_block_size( const mbedtls_cipher_context_t *ctx )
+static inline unsigned int mbedtls_cipher_get_block_size(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
+    if( ctx->cipher_info == NULL )
         return 0;
 
     return ctx->cipher_info->block_size;
@@ -427,14 +438,16 @@ static inline unsigned int mbedtls_cipher_get_block_size( const mbedtls_cipher_c
  * \brief        This function returns the mode of operation for
  *               the cipher. For example, MBEDTLS_MODE_CBC.
  *
- * \param ctx    The context of the cipher. Must be initialized.
+ * \param ctx    The context of the cipher. This must be initialized.
  *
  * \return       The mode of operation.
  * \return       #MBEDTLS_MODE_NONE if \p ctx has not been initialized.
  */
-static inline mbedtls_cipher_mode_t mbedtls_cipher_get_cipher_mode( const mbedtls_cipher_context_t *ctx )
+static inline mbedtls_cipher_mode_t mbedtls_cipher_get_cipher_mode(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, MBEDTLS_MODE_NONE );
+    if( ctx->cipher_info == NULL )
         return MBEDTLS_MODE_NONE;
 
     return ctx->cipher_info->mode;
@@ -444,15 +457,17 @@ static inline mbedtls_cipher_mode_t mbedtls_cipher_get_cipher_mode( const mbedtl
  * \brief       This function returns the size of the IV or nonce
  *              of the cipher, in Bytes.
  *
- * \param ctx   The context of the cipher. Must be initialized.
+ * \param ctx   The context of the cipher. This must be initialized.
  *
  * \return      The recommended IV size if no IV has been set.
  * \return      \c 0 for ciphers not using an IV or a nonce.
  * \return      The actual size if an IV has been set.
  */
-static inline int mbedtls_cipher_get_iv_size( const mbedtls_cipher_context_t *ctx )
+static inline int mbedtls_cipher_get_iv_size(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
+    if( ctx->cipher_info == NULL )
         return 0;
 
     if( ctx->iv_size != 0 )
@@ -464,14 +479,17 @@ static inline int mbedtls_cipher_get_iv_size( const mbedtls_cipher_context_t *ct
 /**
  * \brief               This function returns the type of the given cipher.
  *
- * \param ctx           The context of the cipher. Must be initialized.
+ * \param ctx           The context of the cipher. This must be initialized.
  *
  * \return              The type of the cipher.
  * \return              #MBEDTLS_CIPHER_NONE if \p ctx has not been initialized.
  */
-static inline mbedtls_cipher_type_t mbedtls_cipher_get_type( const mbedtls_cipher_context_t *ctx )
+static inline mbedtls_cipher_type_t mbedtls_cipher_get_type(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET(
+        ctx != NULL, MBEDTLS_CIPHER_NONE );
+    if( ctx->cipher_info == NULL )
         return MBEDTLS_CIPHER_NONE;
 
     return ctx->cipher_info->type;
@@ -481,14 +499,16 @@ static inline mbedtls_cipher_type_t mbedtls_cipher_get_type( const mbedtls_ciphe
  * \brief               This function returns the name of the given cipher
  *                      as a string.
  *
- * \param ctx           The context of the cipher. Must be initialized.
+ * \param ctx           The context of the cipher. This must be initialized.
  *
  * \return              The name of the cipher.
  * \return              NULL if \p ctx has not been not initialized.
  */
-static inline const char *mbedtls_cipher_get_name( const mbedtls_cipher_context_t *ctx )
+static inline const char *mbedtls_cipher_get_name(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET( ctx != NULL, 0 );
+    if( ctx->cipher_info == NULL )
         return 0;
 
     return ctx->cipher_info->name;
@@ -497,15 +517,18 @@ static inline const char *mbedtls_cipher_get_name( const mbedtls_cipher_context_
 /**
  * \brief               This function returns the key length of the cipher.
  *
- * \param ctx           The context of the cipher. Must be initialized.
+ * \param ctx           The context of the cipher. This must be initialized.
  *
  * \return              The key length of the cipher in bits.
  * \return              #MBEDTLS_KEY_LENGTH_NONE if ctx \p has not been
  *                      initialized.
  */
-static inline int mbedtls_cipher_get_key_bitlen( const mbedtls_cipher_context_t *ctx )
+static inline int mbedtls_cipher_get_key_bitlen(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET(
+        ctx != NULL, MBEDTLS_KEY_LENGTH_NONE );
+    if( ctx->cipher_info == NULL )
         return MBEDTLS_KEY_LENGTH_NONE;
 
     return (int) ctx->cipher_info->key_bitlen;
@@ -514,14 +537,17 @@ static inline int mbedtls_cipher_get_key_bitlen( const mbedtls_cipher_context_t
 /**
  * \brief          This function returns the operation of the given cipher.
  *
- * \param ctx      The context of the cipher. Must be initialized.
+ * \param ctx      The context of the cipher. This must be initialized.
  *
  * \return         The type of operation: #MBEDTLS_ENCRYPT or #MBEDTLS_DECRYPT.
  * \return         #MBEDTLS_OPERATION_NONE if \p ctx has not been initialized.
  */
-static inline mbedtls_operation_t mbedtls_cipher_get_operation( const mbedtls_cipher_context_t *ctx )
+static inline mbedtls_operation_t mbedtls_cipher_get_operation(
+    const mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    MBEDTLS_INTERNAL_VALIDATE_RET(
+        ctx != NULL, MBEDTLS_OPERATION_NONE );
+    if( ctx->cipher_info == NULL )
         return MBEDTLS_OPERATION_NONE;
 
     return ctx->operation;
@@ -530,11 +556,11 @@ static inline mbedtls_operation_t mbedtls_cipher_get_operation( const mbedtls_ci
 /**
  * \brief               This function sets the key to use with the given context.
  *
- * \param ctx           The generic cipher context. May not be NULL. Must have
- *                      been initialized using mbedtls_cipher_info_from_type()
- *                      or mbedtls_cipher_info_from_string().
- * \param key           The key to use.
- * \param key_bitlen    The key length to use, in bits.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      bound to a cipher information structure.
+ * \param key           The key to use. This must be a readable buffer of at
+ *                      least \p key_bitlen Bits.
+ * \param key_bitlen    The key length to use, in Bits.
  * \param operation     The operation that the key will be used for:
  *                      #MBEDTLS_ENCRYPT or #MBEDTLS_DECRYPT.
  *
@@ -543,8 +569,10 @@ static inline mbedtls_operation_t mbedtls_cipher_get_operation( const mbedtls_ci
  *                      parameter-verification failure.
  * \return              A cipher-specific error code on failure.
  */
-int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx, const unsigned char *key,
-                   int key_bitlen, const mbedtls_operation_t operation );
+int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx,
+                           const unsigned char *key,
+                           int key_bitlen,
+                           const mbedtls_operation_t operation );
 
 #if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
 /**
@@ -553,7 +581,8 @@ int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx, const unsigned char *k
  *
  *                      The default passing mode is PKCS7 padding.
  *
- * \param ctx           The generic cipher context.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      bound to a cipher information structure.
  * \param mode          The padding mode.
  *
  * \return              \c 0 on success.
@@ -562,7 +591,8 @@ int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx, const unsigned char *k
  * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA if the cipher mode
  *                      does not support padding.
  */
-int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx, mbedtls_cipher_padding_t mode );
+int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx,
+                                     mbedtls_cipher_padding_t mode );
 #endif /* MBEDTLS_CIPHER_MODE_WITH_PADDING */
 
 /**
@@ -572,8 +602,10 @@ int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx, mbedtls_ciph
  * \note            Some ciphers do not use IVs nor nonce. For these
  *                  ciphers, this function has no effect.
  *
- * \param ctx       The generic cipher context.
- * \param iv        The IV to use, or NONCE_COUNTER for CTR-mode ciphers.
+ * \param ctx       The generic cipher context. This must be initialized and
+ *                  bound to a cipher information structure.
+ * \param iv        The IV to use, or NONCE_COUNTER for CTR-mode ciphers. This
+ *                  must be a readable buffer of at least \p iv_len Bytes.
  * \param iv_len    The IV length for ciphers with variable-size IV.
  *                  This parameter is discarded by ciphers with fixed-size IV.
  *
@@ -582,12 +614,13 @@ int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx, mbedtls_ciph
  *                  parameter-verification failure.
  */
 int mbedtls_cipher_set_iv( mbedtls_cipher_context_t *ctx,
-                   const unsigned char *iv, size_t iv_len );
+                           const unsigned char *iv,
+                           size_t iv_len );
 
 /**
  * \brief         This function resets the cipher state.
  *
- * \param ctx     The generic cipher context.
+ * \param ctx     The generic cipher context. This must be initialized.
  *
  * \return        \c 0 on success.
  * \return        #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
@@ -599,11 +632,13 @@ int mbedtls_cipher_reset( mbedtls_cipher_context_t *ctx );
 /**
  * \brief               This function adds additional data for AEAD ciphers.
  *                      Currently supported with GCM and ChaCha20+Poly1305.
- *                      Must be called exactly once, after mbedtls_cipher_reset().
+ *                      This must be called exactly once, after
+ *                      mbedtls_cipher_reset().
  *
- * \param ctx           The generic cipher context.
- * \param ad            The additional data to use.
- * \param ad_len        the Length of \p ad.
+ * \param ctx           The generic cipher context. This must be initialized.
+ * \param ad            The additional data to use. This must be a readable
+ *                      buffer of at least \p ad_len Bytes.
+ * \param ad_len        the Length of \p ad Bytes.
  *
  * \return              \c 0 on success.
  * \return              A specific error code on failure.
@@ -627,14 +662,17 @@ int mbedtls_cipher_update_ad( mbedtls_cipher_context_t *ctx,
  *                      mbedtls_cipher_finish(), must have \p ilen as a
  *                      multiple of the block size of the cipher.
  *
- * \param ctx           The generic cipher context.
- * \param input         The buffer holding the input data.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      bound to a key.
+ * \param input         The buffer holding the input data. This must be a
+ *                      readable buffer of at least \p ilen Bytes.
  * \param ilen          The length of the input data.
- * \param output        The buffer for the output data. Must be able to hold at
- *                      least \p ilen + block_size. Must not be the same buffer
- *                      as input.
+ * \param output        The buffer for the output data. This must be able to
+ *                      hold at least `ilen + block_size`. This must not be the
+ *                      same buffer as \p input.
  * \param olen          The length of the output data, to be updated with the
- *                      actual number of Bytes written.
+ *                      actual number of Bytes written. This must not be
+ *                      \c NULL.
  *
  * \return              \c 0 on success.
  * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
@@ -652,9 +690,12 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
  *                      contained in it is padded to the size of
  *                      the last block, and written to the \p output buffer.
  *
- * \param ctx           The generic cipher context.
- * \param output        The buffer to write data to. Needs block_size available.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      bound to a key.
+ * \param output        The buffer to write data to. This needs to be a writable
+ *                      buffer of at least \p block_size Bytes.
  * \param olen          The length of the data written to the \p output buffer.
+ *                      This may not be \c NULL.
  *
  * \return              \c 0 on success.
  * \return              #MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA on
@@ -672,10 +713,14 @@ int mbedtls_cipher_finish( mbedtls_cipher_context_t *ctx,
 /**
  * \brief               This function writes a tag for AEAD ciphers.
  *                      Currently supported with GCM and ChaCha20+Poly1305.
- *                      Must be called after mbedtls_cipher_finish().
+ *                      This must be called after mbedtls_cipher_finish().
  *
- * \param ctx           The generic cipher context.
- * \param tag           The buffer to write the tag to.
+ * \param ctx           The generic cipher context. This must be initialized,
+ *                      bound to a key, and have just completed a cipher
+ *                      operation through mbedtls_cipher_finish() the tag for
+ *                      which should be written.
+ * \param tag           The buffer to write the tag to. This must be a writable
+ *                      buffer of at least \p tag_len Bytes.
  * \param tag_len       The length of the tag to write.
  *
  * \return              \c 0 on success.
@@ -687,10 +732,11 @@ int mbedtls_cipher_write_tag( mbedtls_cipher_context_t *ctx,
 /**
  * \brief               This function checks the tag for AEAD ciphers.
  *                      Currently supported with GCM and ChaCha20+Poly1305.
- *                      Must be called after mbedtls_cipher_finish().
+ *                      This must be called after mbedtls_cipher_finish().
  *
- * \param ctx           The generic cipher context.
- * \param tag           The buffer holding the tag.
+ * \param ctx           The generic cipher context. This must be initialized.
+ * \param tag           The buffer holding the tag. This must be a readable
+ *                      buffer of at least \p tag_len Bytes.
  * \param tag_len       The length of the tag to check.
  *
  * \return              \c 0 on success.
@@ -704,18 +750,22 @@ int mbedtls_cipher_check_tag( mbedtls_cipher_context_t *ctx,
  * \brief               The generic all-in-one encryption/decryption function,
  *                      for all ciphers except AEAD constructs.
  *
- * \param ctx           The generic cipher context.
+ * \param ctx           The generic cipher context. This must be initialized.
  * \param iv            The IV to use, or NONCE_COUNTER for CTR-mode ciphers.
+ *                      This must be a readable buffer of at least \p iv_len
+ *                      Bytes.
  * \param iv_len        The IV length for ciphers with variable-size IV.
  *                      This parameter is discarded by ciphers with fixed-size
  *                      IV.
- * \param input         The buffer holding the input data.
- * \param ilen          The length of the input data.
- * \param output        The buffer for the output data. Must be able to hold at
- *                      least \p ilen + block_size. Must not be the same buffer
- *                      as input.
+ * \param input         The buffer holding the input data. This must be a
+ *                      readable buffer of at least \p ilen Bytes.
+ * \param ilen          The length of the input data in Bytes.
+ * \param output        The buffer for the output data. This must be able to
+ *                      hold at least `ilen + block_size`. This must not be the
+ *                      same buffer as \p input.
  * \param olen          The length of the output data, to be updated with the
- *                      actual number of Bytes written.
+ *                      actual number of Bytes written. This must not be
+ *                      \c NULL.
  *
  * \note                Some ciphers do not use IVs nor nonce. For these
  *                      ciphers, use \p iv = NULL and \p iv_len = 0.
@@ -738,19 +788,26 @@ int mbedtls_cipher_crypt( mbedtls_cipher_context_t *ctx,
 /**
  * \brief               The generic autenticated encryption (AEAD) function.
  *
- * \param ctx           The generic cipher context.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      bound to a key.
  * \param iv            The IV to use, or NONCE_COUNTER for CTR-mode ciphers.
+ *                      This must be a readable buffer of at least \p iv_len
+ *                      Bytes.
  * \param iv_len        The IV length for ciphers with variable-size IV.
  *                      This parameter is discarded by ciphers with fixed-size IV.
- * \param ad            The additional data to authenticate.
+ * \param ad            The additional data to authenticate. This must be a
+ *                      readable buffer of at least \p ad_len Bytes.
  * \param ad_len        The length of \p ad.
- * \param input         The buffer holding the input data.
+ * \param input         The buffer holding the input data. This must be a
+ *                      readable buffer of at least \p ilen Bytes.
  * \param ilen          The length of the input data.
- * \param output        The buffer for the output data.
- *                      Must be able to hold at least \p ilen.
+ * \param output        The buffer for the output data. This must be able to
+ *                      hold at least \p ilen Bytes.
  * \param olen          The length of the output data, to be updated with the
- *                      actual number of Bytes written.
- * \param tag           The buffer for the authentication tag.
+ *                      actual number of Bytes written. This must not be
+ *                      \c NULL.
+ * \param tag           The buffer for the authentication tag. This must be a
+ *                      writable buffer of at least \p tag_len Bytes.
  * \param tag_len       The desired length of the authentication tag.
  *
  * \return              \c 0 on success.
@@ -772,19 +829,26 @@ int mbedtls_cipher_auth_encrypt( mbedtls_cipher_context_t *ctx,
  *                      is zeroed out to prevent the unauthentic plaintext being
  *                      used, making this interface safer.
  *
- * \param ctx           The generic cipher context.
+ * \param ctx           The generic cipher context. This must be initialized and
+ *                      and bound to a key.
  * \param iv            The IV to use, or NONCE_COUNTER for CTR-mode ciphers.
+ *                      This must be a readable buffer of at least \p iv_len
+ *                      Bytes.
  * \param iv_len        The IV length for ciphers with variable-size IV.
  *                      This parameter is discarded by ciphers with fixed-size IV.
- * \param ad            The additional data to be authenticated.
+ * \param ad            The additional data to be authenticated. This must be a
+ *                      readable buffer of at least \p ad_len Bytes.
  * \param ad_len        The length of \p ad.
- * \param input         The buffer holding the input data.
+ * \param input         The buffer holding the input data. This must be a
+ *                      readable buffer of at least \p ilen Bytes.
  * \param ilen          The length of the input data.
  * \param output        The buffer for the output data.
- *                      Must be able to hold at least \p ilen.
+ *                      This must be able to hold at least \p ilen Bytes.
  * \param olen          The length of the output data, to be updated with the
- *                      actual number of Bytes written.
- * \param tag           The buffer holding the authentication tag.
+ *                      actual number of Bytes written. This must not be
+ *                      \c NULL.
+ * \param tag           The buffer holding the authentication tag. This must be
+ *                      a readable buffer of at least \p tag_len Bytes.
  * \param tag_len       The length of the authentication tag.
  *
  * \return              \c 0 on success.
diff --git a/library/cipher.c b/library/cipher.c
index d7acf34ee5..273997577b 100644
--- a/library/cipher.c
+++ b/library/cipher.c
@@ -65,6 +65,11 @@
 #define mbedtls_free   free
 #endif
 
+#define CIPHER_VALIDATE_RET( cond )    \
+    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA )
+#define CIPHER_VALIDATE( cond )        \
+    MBEDTLS_INTERNAL_VALIDATE( cond )
+
 #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
 /* Compare the contents of two buffers in constant time.
  * Returns 0 if the contents are bitwise identical, otherwise returns
@@ -81,7 +86,7 @@ static int mbedtls_constant_time_memcmp( const void *v1, const void *v2, size_t
     for( diff = 0, i = 0; i < len; i++ )
         diff |= p1[i] ^ p2[i];
 
-    return (int)diff;
+    return( (int)diff );
 }
 #endif /* MBEDTLS_GCM_C || MBEDTLS_CHACHAPOLY_C */
 
@@ -150,6 +155,7 @@ const mbedtls_cipher_info_t *mbedtls_cipher_info_from_values( const mbedtls_ciph
 
 void mbedtls_cipher_init( mbedtls_cipher_context_t *ctx )
 {
+    CIPHER_VALIDATE( ctx != NULL );
     memset( ctx, 0, sizeof( mbedtls_cipher_context_t ) );
 }
 
@@ -175,7 +181,8 @@ void mbedtls_cipher_free( mbedtls_cipher_context_t *ctx )
 
 int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx, const mbedtls_cipher_info_t *cipher_info )
 {
-    if( NULL == cipher_info || NULL == ctx )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    if( cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     memset( ctx, 0, sizeof( mbedtls_cipher_context_t ) );
@@ -199,10 +206,16 @@ int mbedtls_cipher_setup( mbedtls_cipher_context_t *ctx, const mbedtls_cipher_in
     return( 0 );
 }
 
-int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx, const unsigned char *key,
-        int key_bitlen, const mbedtls_operation_t operation )
+int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx,
+                           const unsigned char *key,
+                           int key_bitlen,
+                           const mbedtls_operation_t operation )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( key != NULL );
+    CIPHER_VALIDATE_RET( operation == MBEDTLS_ENCRYPT ||
+                         operation == MBEDTLS_DECRYPT );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     if( ( ctx->cipher_info->flags & MBEDTLS_CIPHER_VARIABLE_KEY_LEN ) == 0 &&
@@ -222,28 +235,27 @@ int mbedtls_cipher_setkey( mbedtls_cipher_context_t *ctx, const unsigned char *k
         MBEDTLS_MODE_OFB == ctx->cipher_info->mode ||
         MBEDTLS_MODE_CTR == ctx->cipher_info->mode )
     {
-        return ctx->cipher_info->base->setkey_enc_func( ctx->cipher_ctx, key,
-                ctx->key_bitlen );
+        return( ctx->cipher_info->base->setkey_enc_func( ctx->cipher_ctx, key,
+                                                         ctx->key_bitlen ) );
     }
 
     if( MBEDTLS_DECRYPT == operation )
-        return ctx->cipher_info->base->setkey_dec_func( ctx->cipher_ctx, key,
-                ctx->key_bitlen );
+        return( ctx->cipher_info->base->setkey_dec_func( ctx->cipher_ctx, key,
+                                                         ctx->key_bitlen ) );
 
     return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 }
 
 int mbedtls_cipher_set_iv( mbedtls_cipher_context_t *ctx,
-                   const unsigned char *iv, size_t iv_len )
+                           const unsigned char *iv,
+                           size_t iv_len )
 {
     size_t actual_iv_size;
-    if( NULL == ctx || NULL == ctx->cipher_info )
-        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    else if( NULL == iv && iv_len != 0  )
-        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    if( NULL == iv && iv_len == 0 )
-        ctx->iv_size = 0;
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( iv_len == 0 || iv != NULL );
+    if( ctx->cipher_info == NULL )
+        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     /* avoid buffer overflow in ctx->iv */
     if( iv_len > MBEDTLS_MAX_IV_LENGTH )
@@ -283,7 +295,8 @@ int mbedtls_cipher_set_iv( mbedtls_cipher_context_t *ctx,
 
 int mbedtls_cipher_reset( mbedtls_cipher_context_t *ctx )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     ctx->unprocessed_len = 0;
@@ -295,14 +308,16 @@ int mbedtls_cipher_reset( mbedtls_cipher_context_t *ctx )
 int mbedtls_cipher_update_ad( mbedtls_cipher_context_t *ctx,
                       const unsigned char *ad, size_t ad_len )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( ad_len == 0 || ad != NULL );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
 #if defined(MBEDTLS_GCM_C)
     if( MBEDTLS_MODE_GCM == ctx->cipher_info->mode )
     {
-        return mbedtls_gcm_starts( (mbedtls_gcm_context *) ctx->cipher_ctx, ctx->operation,
-                           ctx->iv, ctx->iv_size, ad, ad_len );
+        return( mbedtls_gcm_starts( (mbedtls_gcm_context *) ctx->cipher_ctx, ctx->operation,
+                                    ctx->iv, ctx->iv_size, ad, ad_len ) );
     }
 #endif
 
@@ -322,8 +337,8 @@ int mbedtls_cipher_update_ad( mbedtls_cipher_context_t *ctx,
         if ( result != 0 )
             return( result );
 
-        return mbedtls_chachapoly_update_aad( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
-                                                          ad, ad_len );
+        return( mbedtls_chachapoly_update_aad( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
+                                               ad, ad_len ) );
     }
 #endif
 
@@ -335,12 +350,14 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
                    size_t ilen, unsigned char *output, size_t *olen )
 {
     int ret;
-    size_t block_size = 0;
+    size_t block_size;
 
-    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
-    {
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( ilen == 0 || input != NULL );
+    CIPHER_VALIDATE_RET( output != NULL );
+    CIPHER_VALIDATE_RET( olen != NULL );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    }
 
     *olen = 0;
     block_size = mbedtls_cipher_get_block_size( ctx );
@@ -365,8 +382,8 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
     if( ctx->cipher_info->mode == MBEDTLS_MODE_GCM )
     {
         *olen = ilen;
-        return mbedtls_gcm_update( (mbedtls_gcm_context *) ctx->cipher_ctx, ilen, input,
-                           output );
+        return( mbedtls_gcm_update( (mbedtls_gcm_context *) ctx->cipher_ctx, ilen, input,
+                                    output ) );
     }
 #endif
 
@@ -374,14 +391,14 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
     if ( ctx->cipher_info->type == MBEDTLS_CIPHER_CHACHA20_POLY1305 )
     {
         *olen = ilen;
-        return mbedtls_chachapoly_update( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
-                                                      ilen, input, output );
+        return( mbedtls_chachapoly_update( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
+                                           ilen, input, output ) );
     }
 #endif
 
     if ( 0 == block_size )
     {
-        return MBEDTLS_ERR_CIPHER_INVALID_CONTEXT;
+        return( MBEDTLS_ERR_CIPHER_INVALID_CONTEXT );
     }
 
     if( input == output &&
@@ -444,7 +461,7 @@ int mbedtls_cipher_update( mbedtls_cipher_context_t *ctx, const unsigned char *i
         {
             if( 0 == block_size )
             {
-                return MBEDTLS_ERR_CIPHER_INVALID_CONTEXT;
+                return( MBEDTLS_ERR_CIPHER_INVALID_CONTEXT );
             }
 
             /* Encryption: only cache partial blocks
@@ -745,7 +762,10 @@ static int get_no_padding( unsigned char *input, size_t input_len,
 int mbedtls_cipher_finish( mbedtls_cipher_context_t *ctx,
                    unsigned char *output, size_t *olen )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info || NULL == olen )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( output != NULL );
+    CIPHER_VALIDATE_RET( olen != NULL );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     *olen = 0;
@@ -815,8 +835,8 @@ int mbedtls_cipher_finish( mbedtls_cipher_context_t *ctx,
 
         /* Set output size for decryption */
         if( MBEDTLS_DECRYPT == ctx->operation )
-            return ctx->get_padding( output, mbedtls_cipher_get_block_size( ctx ),
-                                     olen );
+            return( ctx->get_padding( output, mbedtls_cipher_get_block_size( ctx ),
+                                      olen ) );
 
         /* Set output size for encryption */
         *olen = mbedtls_cipher_get_block_size( ctx );
@@ -830,10 +850,12 @@ int mbedtls_cipher_finish( mbedtls_cipher_context_t *ctx,
 }
 
 #if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
-int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx, mbedtls_cipher_padding_t mode )
+int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx,
+                                     mbedtls_cipher_padding_t mode )
 {
-    if( NULL == ctx ||
-        MBEDTLS_MODE_CBC != ctx->cipher_info->mode )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+
+    if( NULL == ctx->cipher_info || MBEDTLS_MODE_CBC != ctx->cipher_info->mode )
     {
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
     }
@@ -881,7 +903,9 @@ int mbedtls_cipher_set_padding_mode( mbedtls_cipher_context_t *ctx, mbedtls_ciph
 int mbedtls_cipher_write_tag( mbedtls_cipher_context_t *ctx,
                       unsigned char *tag, size_t tag_len )
 {
-    if( NULL == ctx || NULL == ctx->cipher_info || NULL == tag )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( tag_len == 0 || tag != NULL );
+    if( ctx->cipher_info == NULL )
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
     if( MBEDTLS_ENCRYPT != ctx->operation )
@@ -889,7 +913,8 @@ int mbedtls_cipher_write_tag( mbedtls_cipher_context_t *ctx,
 
 #if defined(MBEDTLS_GCM_C)
     if( MBEDTLS_MODE_GCM == ctx->cipher_info->mode )
-        return mbedtls_gcm_finish( (mbedtls_gcm_context *) ctx->cipher_ctx, tag, tag_len );
+        return( mbedtls_gcm_finish( (mbedtls_gcm_context *) ctx->cipher_ctx,
+                                    tag, tag_len ) );
 #endif
 
 #if defined(MBEDTLS_CHACHAPOLY_C)
@@ -899,8 +924,8 @@ int mbedtls_cipher_write_tag( mbedtls_cipher_context_t *ctx,
         if ( tag_len != 16U )
             return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-        return mbedtls_chachapoly_finish( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
-                                                      tag );
+        return( mbedtls_chachapoly_finish( (mbedtls_chachapoly_context*) ctx->cipher_ctx,
+                                           tag ) );
     }
 #endif
 
@@ -913,8 +938,12 @@ int mbedtls_cipher_check_tag( mbedtls_cipher_context_t *ctx,
     unsigned char check_tag[16];
     int ret;
 
-    if( NULL == ctx || NULL == ctx->cipher_info ||
-        MBEDTLS_DECRYPT != ctx->operation )
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( tag_len == 0 || tag != NULL );
+    if( ctx->cipher_info == NULL )
+        return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
+    if( MBEDTLS_DECRYPT != ctx->operation )
     {
         return( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
     }
@@ -976,6 +1005,12 @@ int mbedtls_cipher_crypt( mbedtls_cipher_context_t *ctx,
     int ret;
     size_t finish_olen;
 
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( iv_len == 0 || iv != NULL );
+    CIPHER_VALIDATE_RET( ilen == 0 || input != NULL );
+    CIPHER_VALIDATE_RET( output != NULL );
+    CIPHER_VALIDATE_RET( olen != NULL );
+
     if( ( ret = mbedtls_cipher_set_iv( ctx, iv, iv_len ) ) != 0 )
         return( ret );
 
@@ -1004,6 +1039,14 @@ int mbedtls_cipher_auth_encrypt( mbedtls_cipher_context_t *ctx,
                          unsigned char *output, size_t *olen,
                          unsigned char *tag, size_t tag_len )
 {
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( iv != NULL );
+    CIPHER_VALIDATE_RET( ad_len == 0 || ad != NULL );
+    CIPHER_VALIDATE_RET( ilen == 0 || input != NULL );
+    CIPHER_VALIDATE_RET( output != NULL );
+    CIPHER_VALIDATE_RET( olen != NULL );
+    CIPHER_VALIDATE_RET( tag_len == 0 || tag != NULL );
+
 #if defined(MBEDTLS_GCM_C)
     if( MBEDTLS_MODE_GCM == ctx->cipher_info->mode )
     {
@@ -1051,6 +1094,14 @@ int mbedtls_cipher_auth_decrypt( mbedtls_cipher_context_t *ctx,
                          unsigned char *output, size_t *olen,
                          const unsigned char *tag, size_t tag_len )
 {
+    CIPHER_VALIDATE_RET( ctx != NULL );
+    CIPHER_VALIDATE_RET( iv != NULL );
+    CIPHER_VALIDATE_RET( ad_len == 0 || ad != NULL );
+    CIPHER_VALIDATE_RET( ilen == 0 || input != NULL );
+    CIPHER_VALIDATE_RET( output != NULL );
+    CIPHER_VALIDATE_RET( olen != NULL );
+    CIPHER_VALIDATE_RET( tag_len == 0 || tag != NULL );
+
 #if defined(MBEDTLS_GCM_C)
     if( MBEDTLS_MODE_GCM == ctx->cipher_info->mode )
     {
diff --git a/library/nist_kw.c b/library/nist_kw.c
index 176af9fe08..317a2426ae 100644
--- a/library/nist_kw.c
+++ b/library/nist_kw.c
@@ -311,7 +311,7 @@ cleanup:
     }
     mbedtls_platform_zeroize( inbuff, KW_SEMIBLOCK_LENGTH * 2 );
     mbedtls_platform_zeroize( outbuff, KW_SEMIBLOCK_LENGTH * 2 );
-    mbedtls_cipher_finish( &ctx->cipher_ctx, NULL, &olen );
+
     return( ret );
 }
 
@@ -528,7 +528,7 @@ cleanup:
     mbedtls_platform_zeroize( &bad_padding, sizeof( bad_padding) );
     mbedtls_platform_zeroize( &diff, sizeof( diff ) );
     mbedtls_platform_zeroize( A, sizeof( A ) );
-    mbedtls_cipher_finish( &ctx->cipher_ctx, NULL, &olen );
+
     return( ret );
 }
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 9e15249ea5..eae1f57819 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -72,6 +72,7 @@ add_test_suite(cipher cipher.chacha20)
 add_test_suite(cipher cipher.chachapoly)
 add_test_suite(cipher cipher.des)
 add_test_suite(cipher cipher.gcm)
+add_test_suite(cipher cipher.misc)
 add_test_suite(cipher cipher.null)
 add_test_suite(cipher cipher.padding)
 add_test_suite(cmac)
diff --git a/tests/suites/test_suite_cipher.function b/tests/suites/test_suite_cipher.function
index c5bce7e50f..773c792cac 100644
--- a/tests/suites/test_suite_cipher.function
+++ b/tests/suites/test_suite_cipher.function
@@ -22,72 +22,464 @@ void mbedtls_cipher_list(  )
 /* END_CASE */
 
 /* BEGIN_CASE */
-void cipher_null_args(  )
+void cipher_invalid_param_unconditional( )
 {
-    mbedtls_cipher_context_t ctx;
-    const mbedtls_cipher_info_t *info = mbedtls_cipher_info_from_type( *( mbedtls_cipher_list() ) );
-    unsigned char buf[1] = { 0 };
-    size_t olen;
+    mbedtls_cipher_context_t valid_ctx;
+    mbedtls_cipher_context_t invalid_ctx;
+    mbedtls_operation_t valid_operation = MBEDTLS_ENCRYPT;
+    mbedtls_cipher_padding_t valid_mode = MBEDTLS_PADDING_ZEROS;
+    unsigned char valid_buffer[] = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };
+    int valid_size = sizeof(valid_buffer);
+    int valid_bitlen = valid_size * 8;
+    const mbedtls_cipher_info_t *valid_info = mbedtls_cipher_info_from_type(
+        *( mbedtls_cipher_list() ) );
+    size_t size_t_var;
 
-    mbedtls_cipher_init( &ctx );
+    (void)valid_mode; /* In some configurations this is unused */
 
-    TEST_ASSERT( mbedtls_cipher_get_block_size( NULL ) == 0 );
-    TEST_ASSERT( mbedtls_cipher_get_block_size( &ctx ) == 0 );
+    mbedtls_cipher_init( &valid_ctx );
+    mbedtls_cipher_setup( &valid_ctx, valid_info );
+    mbedtls_cipher_init( &invalid_ctx );
 
-    TEST_ASSERT( mbedtls_cipher_get_cipher_mode( NULL ) == MBEDTLS_MODE_NONE );
-    TEST_ASSERT( mbedtls_cipher_get_cipher_mode( &ctx ) == MBEDTLS_MODE_NONE );
+    /* mbedtls_cipher_setup() */
+    TEST_ASSERT( mbedtls_cipher_setup( &valid_ctx, NULL ) ==
+                 MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    TEST_ASSERT( mbedtls_cipher_get_iv_size( NULL ) == 0 );
-    TEST_ASSERT( mbedtls_cipher_get_iv_size( &ctx ) == 0 );
+    /* mbedtls_cipher_get_block_size() */
+    TEST_ASSERT( mbedtls_cipher_get_block_size( &invalid_ctx ) == 0 );
 
-    TEST_ASSERT( mbedtls_cipher_info_from_string( NULL ) == NULL );
+    /* mbedtls_cipher_get_cipher_mode() */
+    TEST_ASSERT( mbedtls_cipher_get_cipher_mode( &invalid_ctx ) ==
+                 MBEDTLS_MODE_NONE );
 
-    TEST_ASSERT( mbedtls_cipher_setup( &ctx, NULL )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_setup( NULL, info )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_get_iv_size() */
+    TEST_ASSERT( mbedtls_cipher_get_iv_size( &invalid_ctx ) == 0 );
 
-    TEST_ASSERT( mbedtls_cipher_setkey( NULL, buf, 0, MBEDTLS_ENCRYPT )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_setkey( &ctx, buf, 0, MBEDTLS_ENCRYPT )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_get_type() */
+    TEST_ASSERT(
+        mbedtls_cipher_get_type( &invalid_ctx ) ==
+        MBEDTLS_CIPHER_NONE);
 
-    TEST_ASSERT( mbedtls_cipher_set_iv( NULL, buf, 0 )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_set_iv( &ctx, buf, 0 )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_get_name() */
+    TEST_ASSERT( mbedtls_cipher_get_name( &invalid_ctx ) == 0 );
 
-    TEST_ASSERT( mbedtls_cipher_reset( NULL ) == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_reset( &ctx ) == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_get_key_bitlen() */
+    TEST_ASSERT( mbedtls_cipher_get_key_bitlen( &invalid_ctx ) ==
+                 MBEDTLS_KEY_LENGTH_NONE );
+
+    /* mbedtls_cipher_get_operation() */
+    TEST_ASSERT( mbedtls_cipher_get_operation( &invalid_ctx ) ==
+                 MBEDTLS_OPERATION_NONE );
+
+    /* mbedtls_cipher_setkey() */
+    TEST_ASSERT(
+        mbedtls_cipher_setkey( &invalid_ctx,
+                               valid_buffer,
+                               valid_bitlen,
+                               valid_operation ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
+    /* mbedtls_cipher_set_iv() */
+    TEST_ASSERT(
+        mbedtls_cipher_set_iv( &invalid_ctx,
+                               valid_buffer,
+                               valid_size ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+
+    /* mbedtls_cipher_reset() */
+    TEST_ASSERT( mbedtls_cipher_reset( &invalid_ctx ) ==
+                 MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
 #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
-    TEST_ASSERT( mbedtls_cipher_update_ad( NULL, buf, 0 )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_update_ad( &ctx, buf, 0 )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_update_ad() */
+    TEST_ASSERT(
+        mbedtls_cipher_update_ad( &invalid_ctx,
+                                  valid_buffer,
+                                  valid_size ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+#endif /* defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C) */
+
+#if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
+    /* mbedtls_cipher_set_padding_mode() */
+    TEST_ASSERT( mbedtls_cipher_set_padding_mode( &invalid_ctx, valid_mode ) ==
+                 MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 #endif
 
-    TEST_ASSERT( mbedtls_cipher_update( NULL, buf, 0, buf, &olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_update( &ctx, buf, 0, buf, &olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_update() */
+    TEST_ASSERT(
+        mbedtls_cipher_update( &invalid_ctx,
+                               valid_buffer,
+                               valid_size,
+                               valid_buffer,
+                               &size_t_var ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    TEST_ASSERT( mbedtls_cipher_finish( NULL, buf, &olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_finish( &ctx, buf, &olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_finish() */
+    TEST_ASSERT(
+        mbedtls_cipher_finish( &invalid_ctx,
+                               valid_buffer,
+                               &size_t_var ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
 #if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
-    TEST_ASSERT( mbedtls_cipher_write_tag( NULL, buf, olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_write_tag( &ctx, buf, olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_write_tag() */
+    TEST_ASSERT(
+        mbedtls_cipher_write_tag( &invalid_ctx,
+                                  valid_buffer,
+                                  valid_size ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
 
-    TEST_ASSERT( mbedtls_cipher_check_tag( NULL, buf, olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
-    TEST_ASSERT( mbedtls_cipher_check_tag( &ctx, buf, olen )
-                 == MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+    /* mbedtls_cipher_check_tag() */
+    TEST_ASSERT(
+        mbedtls_cipher_check_tag( &invalid_ctx,
+                                  valid_buffer,
+                                  valid_size ) ==
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA );
+#endif /* defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C) */
+
+exit:
+    mbedtls_cipher_free( &invalid_ctx );
+    mbedtls_cipher_free( &valid_ctx );
+}
+/* END_CASE */
+
+/* BEGIN_CASE depends_on:MBEDTLS_CHECK_PARAMS:!MBEDTLS_PARAM_FAILED_ALT */
+void cipher_invalid_param_conditional( )
+{
+    mbedtls_cipher_context_t valid_ctx;
+
+    mbedtls_operation_t valid_operation = MBEDTLS_ENCRYPT;
+    mbedtls_operation_t invalid_operation = 100;
+    mbedtls_cipher_padding_t valid_mode = MBEDTLS_PADDING_ZEROS;
+    unsigned char valid_buffer[] = { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07 };
+    int valid_size = sizeof(valid_buffer);
+    int valid_bitlen = valid_size * 8;
+    const mbedtls_cipher_info_t *valid_info = mbedtls_cipher_info_from_type(
+        *( mbedtls_cipher_list() ) );
+
+    size_t size_t_var;
+
+    (void)valid_mode; /* In some configurations this is unused */
+
+    /* mbedtls_cipher_init() */
+    TEST_VALID_PARAM( mbedtls_cipher_init( &valid_ctx ) );
+    TEST_INVALID_PARAM( mbedtls_cipher_init( NULL ) );
+
+    /* mbedtls_cipher_setup() */
+    TEST_VALID_PARAM( mbedtls_cipher_setup( &valid_ctx, valid_info ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_setup( NULL, valid_info ) );
+
+    /* mbedtls_cipher_get_block_size() */
+    TEST_INVALID_PARAM_RET( 0, mbedtls_cipher_get_block_size( NULL ) );
+
+    /* mbedtls_cipher_get_cipher_mode() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_MODE_NONE,
+        mbedtls_cipher_get_cipher_mode( NULL ) );
+
+    /* mbedtls_cipher_get_iv_size() */
+    TEST_INVALID_PARAM_RET( 0, mbedtls_cipher_get_iv_size( NULL ) );
+
+    /* mbedtls_cipher_get_type() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_CIPHER_NONE,
+        mbedtls_cipher_get_type( NULL ) );
+
+    /* mbedtls_cipher_get_name() */
+    TEST_INVALID_PARAM_RET( 0, mbedtls_cipher_get_name( NULL ) );
+
+    /* mbedtls_cipher_get_key_bitlen() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_KEY_LENGTH_NONE,
+        mbedtls_cipher_get_key_bitlen( NULL ) );
+
+    /* mbedtls_cipher_get_operation() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_OPERATION_NONE,
+        mbedtls_cipher_get_operation( NULL ) );
+
+    /* mbedtls_cipher_setkey() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_setkey( NULL,
+                               valid_buffer,
+                               valid_bitlen,
+                               valid_operation ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_setkey( &valid_ctx,
+                               NULL,
+                               valid_bitlen,
+                               valid_operation ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_setkey( &valid_ctx,
+                               valid_buffer,
+                               valid_bitlen,
+                               invalid_operation ) );
+
+    /* mbedtls_cipher_set_iv() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_set_iv( NULL,
+                               valid_buffer,
+                               valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_set_iv( &valid_ctx,
+                               NULL,
+                               valid_size ) );
+
+    /* mbedtls_cipher_reset() */
+    TEST_INVALID_PARAM_RET( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+                            mbedtls_cipher_reset( NULL ) );
+
+#if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
+    /* mbedtls_cipher_update_ad() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update_ad( NULL,
+                                  valid_buffer,
+                                  valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update_ad( &valid_ctx,
+                                  NULL,
+                                  valid_size ) );
+#endif /* defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C) */
+
+#if defined(MBEDTLS_CIPHER_MODE_WITH_PADDING)
+    /* mbedtls_cipher_set_padding_mode() */
+    TEST_INVALID_PARAM_RET( MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+                            mbedtls_cipher_set_padding_mode( NULL, valid_mode ) );
 #endif
+
+    /* mbedtls_cipher_update() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update( NULL,
+                               valid_buffer,
+                               valid_size,
+                               valid_buffer,
+                               &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update( &valid_ctx,
+                               NULL, valid_size,
+                               valid_buffer,
+                               &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update( &valid_ctx,
+                               valid_buffer, valid_size,
+                               NULL,
+                               &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_update( &valid_ctx,
+                               valid_buffer, valid_size,
+                               valid_buffer,
+                               NULL ) );
+
+    /* mbedtls_cipher_finish() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_finish( NULL,
+                               valid_buffer,
+                               &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_finish( &valid_ctx,
+                               NULL,
+                               &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_finish( &valid_ctx,
+                               valid_buffer,
+                               NULL ) );
+
+#if defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C)
+    /* mbedtls_cipher_write_tag() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_write_tag( NULL,
+                                  valid_buffer,
+                                  valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_write_tag( &valid_ctx,
+                                  NULL,
+                                  valid_size ) );
+
+    /* mbedtls_cipher_check_tag() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_check_tag( NULL,
+                                  valid_buffer,
+                                  valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_check_tag( &valid_ctx,
+                                  NULL,
+                                  valid_size ) );
+#endif /* defined(MBEDTLS_GCM_C) || defined(MBEDTLS_CHACHAPOLY_C) */
+
+    /* mbedtls_cipher_crypt() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_crypt( NULL,
+                              valid_buffer, valid_size,
+                              valid_buffer, valid_size,
+                              valid_buffer, &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_crypt( &valid_ctx,
+                              NULL, valid_size,
+                              valid_buffer, valid_size,
+                              valid_buffer, &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_crypt( &valid_ctx,
+                              valid_buffer, valid_size,
+                              NULL, valid_size,
+                              valid_buffer, &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_crypt( &valid_ctx,
+                              valid_buffer, valid_size,
+                              valid_buffer, valid_size,
+                              NULL, &size_t_var ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_crypt( &valid_ctx,
+                              valid_buffer, valid_size,
+                              valid_buffer, valid_size,
+                              valid_buffer, NULL ) );
+
+#if defined(MBEDTLS_CIPHER_MODE_AEAD)
+    /* mbedtls_cipher_auth_encrypt() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( NULL,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     NULL, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     NULL, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     NULL, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     NULL, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, NULL,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_encrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     NULL, valid_size ) );
+
+    /* mbedtls_cipher_auth_decrypt() */
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( NULL,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     NULL, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     NULL, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     NULL, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     NULL, &size_t_var,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, NULL,
+                                     valid_buffer, valid_size ) );
+    TEST_INVALID_PARAM_RET(
+        MBEDTLS_ERR_CIPHER_BAD_INPUT_DATA,
+        mbedtls_cipher_auth_decrypt( &valid_ctx,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, valid_size,
+                                     valid_buffer, &size_t_var,
+                                     NULL, valid_size ) );
+#endif /* defined(MBEDTLS_CIPHER_MODE_AEAD) */
+
+    /* mbedtls_cipher_free() */
+    TEST_VALID_PARAM( mbedtls_cipher_free( NULL ) );
+exit:
+    TEST_VALID_PARAM( mbedtls_cipher_free( &valid_ctx ) );
 }
 /* END_CASE */
 
diff --git a/tests/suites/test_suite_cipher.misc.data b/tests/suites/test_suite_cipher.misc.data
new file mode 100644
index 0000000000..25bfd407df
--- /dev/null
+++ b/tests/suites/test_suite_cipher.misc.data
@@ -0,0 +1,5 @@
+CIPHER - Conditional invalid parameter checks
+cipher_invalid_param_conditional:
+
+CIPHER - Unconditional invalid parameter checks
+cipher_invalid_param_unconditional:
diff --git a/tests/suites/test_suite_cipher.padding.data b/tests/suites/test_suite_cipher.padding.data
index 1c0ba09801..dc4c9d70b5 100644
--- a/tests/suites/test_suite_cipher.padding.data
+++ b/tests/suites/test_suite_cipher.padding.data
@@ -1,9 +1,6 @@
 Cipher list
 mbedtls_cipher_list:
 
-Cipher null/uninitialised arguments
-cipher_null_args:
-
 Set padding with AES-CBC
 depends_on:MBEDTLS_AES_C:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_CIPHER_PADDING_PKCS7
 set_padding:MBEDTLS_CIPHER_AES_128_CBC:MBEDTLS_PADDING_PKCS7:0