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Outsource code for generating PKCS1 v1.5 encoding
This commit moves the code preparing PKCS1 v1.5 encoded hashes from `mbedtls_rsa_rsassa_pkcs1_v15_sign` to a separate non-public function `rsa_rsassa_pkcs1_v15_encode`. This code-path will then be re-used by the signature verification function `mbetls_rsa_rsassa_pkcs1_v15_verify` in a later commit.
This commit is contained in:
Hanno Becker
parent
171a8f1c95
commit
fdf38030de
208
library/rsa.c
208
library/rsa.c
@ -1160,6 +1160,138 @@ int mbedtls_rsa_rsassa_pss_sign( mbedtls_rsa_context *ctx,
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/*
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* Implementation of the PKCS#1 v2.1 RSASSA-PKCS1-V1_5-SIGN function
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*/
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/* Construct a PKCS v1.5 encoding of a hashed message
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*
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* This is used both for signature generation and verification.
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*
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* Parameters:
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* - md_alg: Identifies the hash algorithm used to generate the given hash;
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* MBEDTLS_MD_NONE if raw data are signed.
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* - hashlen: Length of hash in case hashlen is MBEDTLS_MD_NONE.
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* - hash: Buffer containing the hashed message.
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* - sig_len: Length of the encoded message.
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* - dst: Buffer to hold the encoded message.
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*
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* Assumptions:
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* - hash has size hashlen if md_alg == MBEDTLS_MD_NONE.
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* - hash has size corresponding to md_alg if md_alg != MBEDTLS_MD_NONE.
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* - dst points to a buffer of size at least sig_len.
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*
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*/
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static int rsa_rsassa_pkcs1_v15_encode( mbedtls_md_type_t md_alg,
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unsigned int hashlen,
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const unsigned char *hash,
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size_t sig_len,
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unsigned char *dst )
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{
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size_t oid_size = 0;
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size_t nb_pad = sig_len;
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unsigned char *p = dst;
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const char *oid = NULL;
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/* Are we signing hashed or raw data? */
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if( md_alg != MBEDTLS_MD_NONE )
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{
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const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( md_alg );
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if( md_info == NULL )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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if( mbedtls_oid_get_oid_by_md( md_alg, &oid, &oid_size ) != 0 )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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hashlen = mbedtls_md_get_size( md_info );
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/* Double-check that 8 + hashlen + oid_size can be used as a
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* 1-byte ASN.1 length encoding and that there's no overflow. */
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if( 8 + hashlen + oid_size >= 0x80 ||
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10 + hashlen < hashlen ||
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10 + hashlen + oid_size < 10 + hashlen )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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/*
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* Static bounds check:
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* - Need 10 bytes for five tag-length pairs.
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* (Insist on 1-byte length encodings to protect against variants of
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* Bleichenbacher's forgery attack against lax PKCS#1v1.5 verification)
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* - Need hashlen bytes for hash
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* - Need oid_size bytes for hash alg OID.
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*/
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if( nb_pad < 10 + hashlen + oid_size )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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nb_pad -= 10 + hashlen + oid_size;
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}
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else
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{
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if( nb_pad < hashlen )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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nb_pad -= hashlen;
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}
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/* Signature header and padding delimiter */
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if( nb_pad < 3 )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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nb_pad -= 3;
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/* Now nb_pad is the amount of memory to be filled
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* with padding; must be at least 8 bytes. */
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if( nb_pad < 8 )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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/* Write signature header and padding */
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*p++ = 0;
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*p++ = MBEDTLS_RSA_SIGN;
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memset( p, 0xFF, nb_pad );
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p += nb_pad;
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*p++ = 0;
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/* Are we signing raw data? */
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if( md_alg == MBEDTLS_MD_NONE )
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{
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memcpy( p, hash, hashlen );
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return( 0 );
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}
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/* Signing hashed data, add corresponding ASN.1 structure
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*
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* DigestInfo ::= SEQUENCE {
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* digestAlgorithm DigestAlgorithmIdentifier,
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* digest Digest }
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* DigestAlgorithmIdentifier ::= AlgorithmIdentifier
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* Digest ::= OCTET STRING
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*
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* Schematic:
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* TAG-SEQ + LEN [ TAG-SEQ + LEN [ TAG-OID + LEN [ OID ]
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* TAG-NULL + LEN [ NULL ] ]
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* TAG-OCTET + LEN [ HASH ] ]
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*/
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*p++ = MBEDTLS_ASN1_SEQUENCE | MBEDTLS_ASN1_CONSTRUCTED;
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*p++ = 0x08 + oid_size + hashlen;
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*p++ = MBEDTLS_ASN1_SEQUENCE | MBEDTLS_ASN1_CONSTRUCTED;
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*p++ = 0x04 + oid_size;
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*p++ = MBEDTLS_ASN1_OID;
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*p++ = oid_size;
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memcpy( p, oid, oid_size );
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p += oid_size;
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*p++ = MBEDTLS_ASN1_NULL;
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*p++ = 0x00;
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*p++ = MBEDTLS_ASN1_OCTET_STRING;
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*p++ = hashlen;
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memcpy( p, hash, hashlen );
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p += hashlen;
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/* Just a sanity-check, should be automatic
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* after the initial bounds check. */
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if( p != dst + sig_len )
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{
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mbedtls_zeroize( dst, sig_len );
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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}
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return( 0 );
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}
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/*
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* Do an RSA operation to sign the message digest
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*/
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@ -1172,80 +1304,36 @@ int mbedtls_rsa_rsassa_pkcs1_v15_sign( mbedtls_rsa_context *ctx,
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const unsigned char *hash,
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unsigned char *sig )
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{
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size_t nb_pad, olen, oid_size = 0;
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unsigned char *p = sig;
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const char *oid = NULL;
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unsigned char *sig_try = NULL, *verif = NULL;
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int ret;
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unsigned char *sig_try = NULL, *verif = NULL;
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if( mode == MBEDTLS_RSA_PRIVATE && ctx->padding != MBEDTLS_RSA_PKCS_V15 )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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olen = ctx->len;
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nb_pad = olen - 3;
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if( md_alg != MBEDTLS_MD_NONE )
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{
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const mbedtls_md_info_t *md_info = mbedtls_md_info_from_type( md_alg );
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if( md_info == NULL )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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if( mbedtls_oid_get_oid_by_md( md_alg, &oid, &oid_size ) != 0 )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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nb_pad -= 10 + oid_size;
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hashlen = mbedtls_md_get_size( md_info );
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}
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nb_pad -= hashlen;
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if( ( nb_pad < 8 ) || ( nb_pad > olen ) )
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return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
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*p++ = 0;
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*p++ = MBEDTLS_RSA_SIGN;
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memset( p, 0xFF, nb_pad );
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p += nb_pad;
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*p++ = 0;
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if( md_alg == MBEDTLS_MD_NONE )
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{
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memcpy( p, hash, hashlen );
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}
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else
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{
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/*
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* DigestInfo ::= SEQUENCE {
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* digestAlgorithm DigestAlgorithmIdentifier,
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* digest Digest }
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*
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* DigestAlgorithmIdentifier ::= AlgorithmIdentifier
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*
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* Digest ::= OCTET STRING
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* Prepare PKCS1-v1.5 encoding (padding and hash identifier)
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*/
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if( ( ret = rsa_rsassa_pkcs1_v15_encode( md_alg, hashlen, hash,
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ctx->len, sig ) ) != 0 )
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return( ret );
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/*
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* Call respective RSA primitive
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*/
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*p++ = MBEDTLS_ASN1_SEQUENCE | MBEDTLS_ASN1_CONSTRUCTED;
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*p++ = (unsigned char) ( 0x08 + oid_size + hashlen );
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*p++ = MBEDTLS_ASN1_SEQUENCE | MBEDTLS_ASN1_CONSTRUCTED;
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*p++ = (unsigned char) ( 0x04 + oid_size );
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*p++ = MBEDTLS_ASN1_OID;
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*p++ = oid_size & 0xFF;
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memcpy( p, oid, oid_size );
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p += oid_size;
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*p++ = MBEDTLS_ASN1_NULL;
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*p++ = 0x00;
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*p++ = MBEDTLS_ASN1_OCTET_STRING;
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*p++ = hashlen;
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memcpy( p, hash, hashlen );
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}
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if( mode == MBEDTLS_RSA_PUBLIC )
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{
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/* Skip verification on a public key operation */
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return( mbedtls_rsa_public( ctx, sig, sig ) );
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}
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/*
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/* Private key operation
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*
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* In order to prevent Lenstra's attack, make the signature in a
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* temporary buffer and check it before returning it.
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*/
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sig_try = mbedtls_calloc( 1, ctx->len );
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if( sig_try == NULL )
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return( MBEDTLS_ERR_MPI_ALLOC_FAILED );
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