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PK signature function: require exact hash length

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2021-06-22 18:28:13 +02:00
parent e7885e5441
commit 9dbbc297a3
3 changed files with 34 additions and 22 deletions
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7
ChangeLog.d/require-matching-hashlen-rsa.txt
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@ -1,4 +1,5 @@
API changes
* Functions in the RSA module that accept a hashlen parameter now require
it to match the output size of the hash algorithm used, except when
signing raw data.
* Signature functions in the RSA and PK modules now require the hash
length parameter to be the size of the hash input. For RSA signatures
other than raw PKCS#1 v1.5, this must match the output size of the
specified hash algorithm.

25
docs/3.0-migration-guide.d/require-matching-hashlen-rsa.md
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@ -1,13 +1,24 @@
RSA signature functions now require `hashlen` to match the expected value
-------------------------------------------------------------------------
Signature functions now require the hash length to match the expected value
---------------------------------------------------------------------------
This only affects users of the low-level RSA API; users of the high-level PK
API or of the PSA Crypto API are not affected.
This affects users of the PK API as well as users of the low-level API in the RSA module. Users of the PSA API or of the ECDSA module are unaffected.
All the functions in the RSA module that accept a `hashlen` parameter used to
ignore it unless the `md_alg` parameter was `MBEDTLS_MD_NONE`, indicating raw
data was signed. They now require this parameter's value to be equal to the
output size of the hash algorithm used when signing a hash. (The requirements
when signing raw data are unchanged.)
data was signed. The `hashlen` parameter is now always the size that is read
from the `hash` input buffer. This length must be equal to the output size of
the hash algorithm used when signing a hash. (The requirements when signing
raw data are unchanged.) This affects the following functions:
* `mbedtls_rsa_pkcs1_sign`, `mbedtls_rsa_pkcs1_verify`
* `mbedtls_rsa_rsassa_pkcs1_v15_sign`, `mbedtls_rsa_rsassa_pkcs1_v15_verify`
* `mbedtls_rsa_rsassa_pss_sign`, `mbedtls_rsa_rsassa_pss_verify`
* `mbedtls_rsa_rsassa_pss_sign_ext`, `mbedtls_rsa_rsassa_pss_verify_ext`
The signature functions in the PK module no longer accept 0 as the `hash_len` parameter. The `hash_len` parameter is now always the size that is read from the `hash` input buffer. This affects the following functions:
* `mbedtls_pk_sign`, `mbedtls_pk_verify`
* `mbedtls_pk_sign_restartable`, `mbedtls_pk_verify_restartable`
* `mbedtls_pk_verify_ext`
The migration path is to pass the correct value to those functions.

24
include/mbedtls/pk.h
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@ -399,9 +399,17 @@ int mbedtls_pk_can_do( const mbedtls_pk_context *ctx, mbedtls_pk_type_t type );
* \brief Verify signature (including padding if relevant).
*
* \param ctx The PK context to use. It must have been set up.
* \param md_alg Hash algorithm used (see notes)
* \param md_alg Hash algorithm used.
* This can be #MBEDTLS_MD_NONE if the signature algorithm
* does not rely on a hash algorithm (non-deterministic
* ECDSA, RSA PKCS#1 v1.5).
* For PKCS#1 v1.5, if \p md_alg is #MBEDTLS_MD_NONE, then
* \p hash is the DigestInfo structure used by RFC 8017
* &sect;9.2 steps 3&ndash;6. If \p md_alg is a valid hash
* algorithm then \p hash is the digest itself, and this
* function calculates the DigestInfo encoding internally.
* \param hash Hash of the message to sign
* \param hash_len Hash length or 0 (see notes)
* \param hash_len Hash length
* \param sig Signature to verify
* \param sig_len Signature length
*
@ -413,11 +421,6 @@ int mbedtls_pk_can_do( const mbedtls_pk_context *ctx, mbedtls_pk_type_t type );
* \note For RSA keys, the default padding type is PKCS#1 v1.5.
* Use \c mbedtls_pk_verify_ext( MBEDTLS_PK_RSASSA_PSS, ... )
* to verify RSASSA_PSS signatures.
*
* \note If hash_len is 0, then the length associated with md_alg
* is used instead, or an error returned if it is invalid.
*
* \note md_alg may be MBEDTLS_MD_NONE, only if hash_len != 0
*/
int mbedtls_pk_verify( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
const unsigned char *hash, size_t hash_len,
@ -490,7 +493,7 @@ int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
* with a private key.
* \param md_alg Hash algorithm used (see notes)
* \param hash Hash of the message to sign
* \param hash_len Hash length or 0 (see notes)
* \param hash_len Hash length
* \param sig Place to write the signature.
* It must have enough room for the signature.
* #MBEDTLS_PK_SIGNATURE_MAX_SIZE is always enough.
@ -507,9 +510,6 @@ int mbedtls_pk_verify_ext( mbedtls_pk_type_t type, const void *options,
* There is no interface in the PK module to make RSASSA-PSS
* signatures yet.
*
* \note If hash_len is 0, then the length associated with md_alg
* is used instead, or an error returned if it is invalid.
*
* \note For RSA, md_alg may be MBEDTLS_MD_NONE if hash_len != 0.
* For ECDSA, md_alg may never be MBEDTLS_MD_NONE.
*/
@ -530,7 +530,7 @@ int mbedtls_pk_sign( mbedtls_pk_context *ctx, mbedtls_md_type_t md_alg,
* with a private key.
* \param md_alg Hash algorithm used (see notes for mbedtls_pk_sign())
* \param hash Hash of the message to sign
* \param hash_len Hash length or 0 (see notes for mbedtls_pk_sign())
* \param hash_len Hash length
* \param sig Place to write the signature.
* It must have enough room for the signature.
* #MBEDTLS_PK_SIGNATURE_MAX_SIZE is always enough.