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Fix MBEDTLS_PK_SIGNATURE_MAX_SIZE to account for ECDSA

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The original definition of MBEDTLS_PK_SIGNATURE_MAX_SIZE only took RSA
into account. An ECDSA signature may be larger than the maximum
possible RSA signature size, depending on build options; for example
this is the case with config-suite-b.h.
This commit is contained in:
Gilles Peskine 2019-11-05 16:56:39 +01:00
parent a719db8b04
commit b22a24b23f
1 changed files with 30 additions and 0 deletions
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30
include/mbedtls/pk.h
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@ -104,7 +104,37 @@ typedef struct mbedtls_pk_rsassa_pss_options
/** /**
* \brief Maximum size of a signature made by mbedtls_pk_sign(). * \brief Maximum size of a signature made by mbedtls_pk_sign().
*/ */
/* This fallback value is used if there is no software signature support.
* This is possible even if check_config.h is included, for example if
* MBEDTLS_ECDH_C is enabled but neither MBEDTLS_ECDSA_C nor MBEDTLS_RSA_C.
* Use MBEDTLS_MPI_MAX_SIZE which is the maximum size than an RSA-alt
* implementation can produce, assuming that MBEDTLS_MPI_MAX_SIZE is set
* correctly. This is not necessarily the best choice of size and it may
* change in future versions. */
#define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE #define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
#if defined(MBEDTLS_RSA_C) && \
MBEDTLS_MPI_MAX_SIZE > MBEDTLS_PK_SIGNATURE_MAX_SIZE
#undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
#define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_MPI_MAX_SIZE
#endif
#if defined(MBEDTLS_ECDSA_C) && \
MBEDTLS_ECDSA_MAX_LEN > MBEDTLS_PK_SIGNATURE_MAX_SIZE
#undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
#define MBEDTLS_PK_SIGNATURE_MAX_SIZE MBEDTLS_ECDSA_MAX_LEN
#endif
#if defined(MBEDTLS_USE_PSA_CRYPTO) && \
PSA_ASYMMETRIC_SIGNATURE_MAX_SIZE + 11 > MBEDTLS_PK_SIGNATURE_MAX_SIZE
/* PSA_ASYMMETRIC_SIGNATURE_MAX_SIZE is the maximum size of a signature made
* through the PSA API in the PSA representation.
* The Mbed TLS representation is different for ECDSA signatures:
* PSA uses the raw concatenation of r and s,
* whereas Mbed TLS uses the ASN.1 representation (SEQUENCE of two INTEGERs).
* Add the overhead of ASN.1: up to (1+2) + 2 * (1+2+1) for the
* types, lengths (represented by up to 2 bytes), and potential leading
* zeros of the INTEGERs and the SEQUENCE. */
#undef MBEDTLS_PK_SIGNATURE_MAX_SIZE
#define MBEDTLS_PK_SIGNATURE_MAX_SIZE ( PSA_ASYMMETRIC_SIGNATURE_MAX_SIZE + 11 )
#endif
/** /**
* \brief Types for interfacing with the debug module * \brief Types for interfacing with the debug module