diff --git a/ChangeLog.d/MBEDTLS_PSA_HMAC_DRBG_MD_TYPE.txt b/ChangeLog.d/MBEDTLS_PSA_HMAC_DRBG_MD_TYPE.txt new file mode 100644 index 0000000000..079cd741dc --- /dev/null +++ b/ChangeLog.d/MBEDTLS_PSA_HMAC_DRBG_MD_TYPE.txt @@ -0,0 +1,4 @@ +Security + * Unlike previously documented, enabling MBEDTLS_PSA_HMAC_DRBG_MD_TYPE does + not cause the PSA subsystem to use HMAC_DRBG: it uses HMAC_DRBG only when + MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG and MBEDTLS_CTR_DRBG_C are disabled. diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h index 35921412c6..871d54e48b 100644 --- a/include/mbedtls/mbedtls_config.h +++ b/include/mbedtls/mbedtls_config.h @@ -4016,11 +4016,18 @@ * Use HMAC_DRBG with the specified hash algorithm for HMAC_DRBG for the * PSA crypto subsystem. * - * If this option is unset: - * - If CTR_DRBG is available, the PSA subsystem uses it rather than HMAC_DRBG. - * - Otherwise, the PSA subsystem uses HMAC_DRBG with either - * #MBEDTLS_MD_SHA512 or #MBEDTLS_MD_SHA256 based on availability and - * on unspecified heuristics. + * If this option is unset, the library chooses a hash (currently between + * #MBEDTLS_MD_SHA512 and #MBEDTLS_MD_SHA256) based on availability and + * unspecified heuristics. + * + * \note The PSA crypto subsystem uses the first available mechanism amongst + * the following: + * - #MBEDTLS_PSA_CRYPTO_EXTERNAL_RNG if enabled; + * - Entropy from #MBEDTLS_ENTROPY_C plus CTR_DRBG with AES + * if #MBEDTLS_CTR_DRBG_C is enabled; + * - Entropy from #MBEDTLS_ENTROPY_C plus HMAC_DRBG. + * + * A future version may reevaluate the prioritization of DRBG mechanisms. */ //#define MBEDTLS_PSA_HMAC_DRBG_MD_TYPE MBEDTLS_MD_SHA256 diff --git a/library/psa_crypto_random_impl.h b/library/psa_crypto_random_impl.h index 533fb2e940..5b5163111b 100644 --- a/library/psa_crypto_random_impl.h +++ b/library/psa_crypto_random_impl.h @@ -21,13 +21,10 @@ typedef mbedtls_psa_external_random_context_t mbedtls_psa_random_context_t; #include "mbedtls/entropy.h" /* Choose a DRBG based on configuration and availability */ -#if defined(MBEDTLS_PSA_HMAC_DRBG_MD_TYPE) - -#include "mbedtls/hmac_drbg.h" - -#elif defined(MBEDTLS_CTR_DRBG_C) +#if defined(MBEDTLS_CTR_DRBG_C) #include "mbedtls/ctr_drbg.h" +#undef MBEDTLS_PSA_HMAC_DRBG_MD_TYPE #elif defined(MBEDTLS_HMAC_DRBG_C) @@ -49,17 +46,11 @@ typedef mbedtls_psa_external_random_context_t mbedtls_psa_random_context_t; #error "No hash algorithm available for HMAC_DBRG." #endif -#else /* !MBEDTLS_PSA_HMAC_DRBG_MD_TYPE && !MBEDTLS_CTR_DRBG_C && !MBEDTLS_HMAC_DRBG_C*/ +#else /* !MBEDTLS_CTR_DRBG_C && !MBEDTLS_HMAC_DRBG_C*/ #error "No DRBG module available for the psa_crypto module." -#endif /* !MBEDTLS_PSA_HMAC_DRBG_MD_TYPE && !MBEDTLS_CTR_DRBG_C && !MBEDTLS_HMAC_DRBG_C*/ - -#if defined(MBEDTLS_CTR_DRBG_C) -#include "mbedtls/ctr_drbg.h" -#elif defined(MBEDTLS_HMAC_DRBG_C) -#include "mbedtls/hmac_drbg.h" -#endif /* !MBEDTLS_CTR_DRBG_C && !MBEDTLS_HMAC_DRBG_C */ +#endif /* !MBEDTLS_CTR_DRBG_C && !MBEDTLS_HMAC_DRBG_C*/ /* The maximum number of bytes that mbedtls_psa_get_random() is expected to return. */ #if defined(MBEDTLS_CTR_DRBG_C)