Add inverse key function

Signed-off-by: Jerry Yu <jerry.h.yu@arm.com>

library/aes.c

@@ -661,6 +661,16 @@ int mbedtls_aes_setkey_dec(mbedtls_aes_context *ctx, const unsigned char *key,
     }
 #endif
 
+#if defined(MBEDTLS_AESCE_C) && defined(MBEDTLS_HAVE_ARM64)
+    if (mbedtls_aesce_has_support()) {
+        mbedtls_aesce_inverse_key(
+            (unsigned char *) RK,
+            (const unsigned char *) (cty.buf + cty.rk_offset),
+            ctx->nr);
+        goto exit;
+    }
+#endif
+
     SK = cty.buf + cty.rk_offset + cty.nr * 4;
 
     *RK++ = *SK++;

library/aesce.c

@@ -66,6 +66,24 @@ int mbedtls_aesce_has_support(void)
 }
 
 
+/*
+ * Compute decryption round keys from encryption round keys
+ */
+void mbedtls_aesce_inverse_key(unsigned char *invkey,
+                               const unsigned char *fwdkey,
+                               int nr)
+{
+    int i, j;
+    j = nr;
+    vst1q_u8(invkey, vld1q_u8(fwdkey + j * 16));
+    for (i = 1, j--; j > 0; i++, j--) {
+        vst1q_u8(invkey + i * 16,
+                 vaesimcq_u8(vld1q_u8(fwdkey + j * 16)));
+    }
+    vst1q_u8(invkey + i * 16, vld1q_u8(fwdkey + j * 16));
+
+}
+
 static uint8_t const rcon[] = { 0x01, 0x02, 0x04, 0x08, 0x10,
                                 0x20, 0x40, 0x80, 0x1b, 0x36 };
 

library/aesce.h

@@ -50,6 +50,18 @@ extern "C" {
 int mbedtls_aesce_has_support(void);
 
 
+/**
+ * \brief           Internal round key inversion. This function computes
+ *                  decryption round keys from the encryption round keys.
+ *
+ * \param invkey    Round keys for the equivalent inverse cipher
+ * \param fwdkey    Original round keys (for encryption)
+ * \param nr        Number of rounds (that is, number of round keys minus one)
+ */
+void mbedtls_aesce_inverse_key(unsigned char *invkey,
+                               const unsigned char *fwdkey,
+                               int nr);
+
 /**
  * \brief           Internal key expansion for encryption
  *