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Remove secp256k1 from the default X.509 and TLS profiles

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For TLS, secp256k1 is deprecated by RFC 8422 §5.1.1. For X.509,
secp256k1 is not deprecated, but it isn't used in practice, especially
in the context of TLS where there isn't much point in having an X.509
certificate which most peers do not support. So remove it from the
default profile. We can add it back later if there is demand.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-17 23:17:52 +02:00
parent a03fb29666
commit 39957503c5
4 changed files with 5 additions and 6 deletions
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2
docs/3.0-migration-guide.d/default-curves.md
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@ -7,6 +7,8 @@ Hashes and curves weaker than 255 bits (security strength less than 128 bits) ar
The compile-time options `MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_CERTIFICATES` and `MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE` are no longer available.
The curve secp256k1 has also been removed from the default X.509 and TLS profiles. [RFC 8422](https://datatracker.ietf.org/doc/html/rfc8422#section-5.1.1) deprecates it in TLS, and it is very rarely used, although it is not known to be weak at the time of writing.
If you still need to accept certificates signed with algorithms that have been removed from the default profile, call `mbedtls_x509_crt_verify_with_profile` instead of `mbedtls_x509_crt_verify` and pass a profile that allows the curves and hashes you want. For example, to allow SHA-224:
```
mbedtls_x509_crt_profile my_profile = mbedtls_x509_crt_profile_default;

4
include/mbedtls/x509_crt.h
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@ -335,11 +335,11 @@ typedef void mbedtls_x509_crt_restart_ctx;
*
* This profile permits:
* - SHA2 hashes with at least 256 bits: SHA-256, SHA-384, SHA-512.
* - Elliptic curves with 255 bits and above.
* - Elliptic curves with 255 bits and above except secp256k1.
* - RSA with 2048 bits and above.
*
* New minor versions of Mbed TLS may extend this profile, for example if
* new curves are added to the library. New minor versions of Mbed TLS will
* new algorithms are added to the library. New minor versions of Mbed TLS will
* not reduce this profile unless serious security concerns require it.
*/
extern const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_default;

3
library/ssl_tls.c
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@ -6131,9 +6131,6 @@ static mbedtls_ecp_group_id ssl_preset_default_curves[] = {
#if defined(MBEDTLS_ECP_DP_SECP256R1_ENABLED)
MBEDTLS_ECP_DP_SECP256R1,
#endif
#if defined(MBEDTLS_ECP_DP_SECP256K1_ENABLED)
MBEDTLS_ECP_DP_SECP256K1,
#endif
#if defined(MBEDTLS_ECP_DP_SECP384R1_ENABLED)
MBEDTLS_ECP_DP_SECP384R1,
#endif

2
library/x509_crt.c
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@ -114,7 +114,7 @@ const mbedtls_x509_crt_profile mbedtls_x509_crt_profile_default =
MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_BP256R1 ) |
MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_BP384R1 ) |
MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_BP512R1 ) |
MBEDTLS_X509_ID_FLAG( MBEDTLS_ECP_DP_SECP256K1 ),
0,
#else
0,
#endif