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Changelog entry and migration guide for hash and curve profile upgrades

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-02 00:07:17 +02:00
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commit 3758fd6b79
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ChangeLog.d/default-curves.txt Normal file
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Default behavior changes
* Some default policies for X.509 certificate verification and TLS have
changed: curves and hashes weaker than 255 bits are no longer accepted
by default.
Removals
* Remove the compile-time option
MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE.

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docs/3.0-migration-guide.d/default-curves.md Normal file
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Weak curves are now disabled by default for X.509 and TLS
---------------------------------------------------------
The default X.509 verification profile (`mbedtls_x509_crt_profile_default`) and the default curve and hash selection have changed. X.509 and TLS now allow the same algorithms by default (except that the X.509 profile only lists curves that support signature verification).
Hashes and curves weaker than 255 bits are no longer accepted by default. The following algorithms have been removed: SHA-1 (formerly only accepted for key exchanges but not for certificate signatures), SHA-224, secp192r1, secp224r1, secp192k1, secp224k1 (weaker hashes were already not accepted).
The compile-time option `MBEDTLS_TLS_DEFAULT_ALLOW_SHA1_IN_KEY_EXCHANGE` is no longer available.
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 you want. For example, to allow SHA-224:
```
mbedtls_x509_crt_profile my_profile = mbedtls_x509_crt_profile_default;
my_profile.allowed_mds |= MBEDTLS_X509_ID_FLAG( MBEDTLS_MD_SHA224 );
```
If you still need to allow hashes and curves in TLS that have been removed from the default configuration, call `mbedtls_ssl_conf_sig_hashes()` and `mbedtls_ssl_conf_curves()` with the desired lists.