Esempio n. 1
0
static int pkcs5_parse_pbkdf2_params( const mbedtls_asn1_buf *params,
                                      mbedtls_asn1_buf *salt, int *iterations,
                                      int *keylen, mbedtls_md_type_t *md_type )
{
    int ret;
    mbedtls_asn1_buf prf_alg_oid;
    unsigned char *p = params->p;
    const unsigned char *end = params->p + params->len;

    if( params->tag != ( MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) )
        return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );
    /*
     *  PBKDF2-params ::= SEQUENCE {
     *    salt              OCTET STRING,
     *    iterationCount    INTEGER,
     *    keyLength         INTEGER OPTIONAL
     *    prf               AlgorithmIdentifier DEFAULT algid-hmacWithSHA1
     *  }
     *
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &salt->len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
        return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT + ret );

    salt->p = p;
    p += salt->len;

    if( ( ret = mbedtls_asn1_get_int( &p, end, iterations ) ) != 0 )
        return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT + ret );

    if( p == end )
        return( 0 );

    if( ( ret = mbedtls_asn1_get_int( &p, end, keylen ) ) != 0 )
    {
        if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
            return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT + ret );
    }

    if( p == end )
        return( 0 );

    if( ( ret = mbedtls_asn1_get_alg_null( &p, end, &prf_alg_oid ) ) != 0 )
        return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT + ret );

    if( MBEDTLS_OID_CMP( MBEDTLS_OID_HMAC_SHA1, &prf_alg_oid ) != 0 )
        return( MBEDTLS_ERR_PKCS5_FEATURE_UNAVAILABLE );

    *md_type = MBEDTLS_MD_SHA1;

    if( p != end )
        return( MBEDTLS_ERR_PKCS5_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

    return( 0 );
}
Esempio n. 2
0
int mbedtls_ecies_read_version(unsigned char **p, const unsigned char *end,
        int *version)
{
    int result = 0;
    if (version == NULL)
    {
        return MBEDTLS_ERR_ECIES_BAD_INPUT_DATA;
    }
    INVOKE_AND_CHECK(result,
        mbedtls_asn1_get_int(p, end, version)
    );
    return result;
}
Esempio n. 3
0
/*
 *  Version  ::=  INTEGER  {  v1(0), v2(1)  }
 */
static int x509_crl_get_version(unsigned char **p,
                                const unsigned char *end,
                                int *ver) {
    int ret;

    if ((ret = mbedtls_asn1_get_int(p, end, ver)) != 0) {
        if (ret == MBEDTLS_ERR_ASN1_UNEXPECTED_TAG) {
            *ver = 0;
            return (0);
        }

        return (MBEDTLS_ERR_X509_INVALID_VERSION + ret);
    }

    return (0);
}
Esempio n. 4
0
/*
 * Parse an unencrypted PKCS#8 encoded private key
 */
static int pk_parse_key_pkcs8_unencrypted_der(
                                    mbedtls_pk_context *pk,
                                    const unsigned char* key,
                                    size_t keylen )
{
    int ret, version;
    size_t len;
    mbedtls_asn1_buf params;
    unsigned char *p = (unsigned char *) key;
    unsigned char *end = p + keylen;
    mbedtls_pk_type_t pk_alg = MBEDTLS_PK_NONE;
    const mbedtls_pk_info_t *pk_info;

    /*
     * This function parses the PrivatKeyInfo object (PKCS#8 v1.2 = RFC 5208)
     *
     *    PrivateKeyInfo ::= SEQUENCE {
     *      version                   Version,
     *      privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
     *      privateKey                PrivateKey,
     *      attributes           [0]  IMPLICIT Attributes OPTIONAL }
     *
     *    Version ::= INTEGER
     *    PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier
     *    PrivateKey ::= OCTET STRING
     *
     *  The PrivateKey OCTET STRING is a SEC1 ECPrivateKey
     */

    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    end = p + len;

    if( ( ret = mbedtls_asn1_get_int( &p, end, &version ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( version != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_VERSION + ret );

    if( ( ret = pk_get_pk_alg( &p, end, &pk_alg, &params ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( len < 1 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_OUT_OF_DATA );

    if( ( pk_info = mbedtls_pk_info_from_type( pk_alg ) ) == NULL )
        return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );

    if( ( ret = mbedtls_pk_setup( pk, pk_info ) ) != 0 )
        return( ret );

#if defined(MBEDTLS_RSA_C)
    if( pk_alg == MBEDTLS_PK_RSA )
    {
        if( ( ret = pk_parse_key_pkcs1_der( mbedtls_pk_rsa( *pk ), p, len ) ) != 0 )
        {
            mbedtls_pk_free( pk );
            return( ret );
        }
    } else
#endif /* MBEDTLS_RSA_C */
#if defined(MBEDTLS_ECP_C)
    if( pk_alg == MBEDTLS_PK_ECKEY || pk_alg == MBEDTLS_PK_ECKEY_DH )
    {
        if( ( ret = pk_use_ecparams( &params, &mbedtls_pk_ec( *pk )->grp ) ) != 0 ||
            ( ret = pk_parse_key_sec1_der( mbedtls_pk_ec( *pk ), p, len )  ) != 0 )
        {
            mbedtls_pk_free( pk );
            return( ret );
        }
    } else
#endif /* MBEDTLS_ECP_C */
        return( MBEDTLS_ERR_PK_UNKNOWN_PK_ALG );

    return( 0 );
}
Esempio n. 5
0
/*
 * Parse a SEC1 encoded private EC key
 */
static int pk_parse_key_sec1_der( mbedtls_ecp_keypair *eck,
                                  const unsigned char *key,
                                  size_t keylen )
{
    int ret;
    int version, pubkey_done;
    size_t len;
    mbedtls_asn1_buf params;
    unsigned char *p = (unsigned char *) key;
    unsigned char *end = p + keylen;
    unsigned char *end2;

    /*
     * RFC 5915, or SEC1 Appendix C.4
     *
     * ECPrivateKey ::= SEQUENCE {
     *      version        INTEGER { ecPrivkeyVer1(1) } (ecPrivkeyVer1),
     *      privateKey     OCTET STRING,
     *      parameters [0] ECParameters {{ NamedCurve }} OPTIONAL,
     *      publicKey  [1] BIT STRING OPTIONAL
     *    }
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    end = p + len;

    if( ( ret = mbedtls_asn1_get_int( &p, end, &version ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( version != 1 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_VERSION );

    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( ( ret = mbedtls_mpi_read_binary( &eck->d, p, len ) ) != 0 )
    {
        mbedtls_ecp_keypair_free( eck );
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    p += len;

    pubkey_done = 0;
    if( p != end )
    {
        /*
         * Is 'parameters' present?
         */
        if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                        MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 0 ) ) == 0 )
        {
            if( ( ret = pk_get_ecparams( &p, p + len, &params) ) != 0 ||
                ( ret = pk_use_ecparams( &params, &eck->grp )  ) != 0 )
            {
                mbedtls_ecp_keypair_free( eck );
                return( ret );
            }
        }
        else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        {
            mbedtls_ecp_keypair_free( eck );
            return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
        }

        /*
         * Is 'publickey' present? If not, or if we can't read it (eg because it
         * is compressed), create it from the private key.
         */
        if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                        MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 1 ) ) == 0 )
        {
            end2 = p + len;

            if( ( ret = mbedtls_asn1_get_bitstring_null( &p, end2, &len ) ) != 0 )
                return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

            if( p + len != end2 )
                return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +
                        MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

            if( ( ret = pk_get_ecpubkey( &p, end2, eck ) ) == 0 )
                pubkey_done = 1;
            else
            {
                /*
                 * The only acceptable failure mode of pk_get_ecpubkey() above
                 * is if the point format is not recognized.
                 */
                if( ret != MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE )
                    return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
            }
        }
        else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        {
            mbedtls_ecp_keypair_free( eck );
            return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
        }
    }

    if( ! pubkey_done &&
        ( ret = mbedtls_ecp_mul( &eck->grp, &eck->Q, &eck->d, &eck->grp.G,
                                                      NULL, NULL ) ) != 0 )
    {
        mbedtls_ecp_keypair_free( eck );
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    if( ( ret = mbedtls_ecp_check_privkey( &eck->grp, &eck->d ) ) != 0 )
    {
        mbedtls_ecp_keypair_free( eck );
        return( ret );
    }

    return( 0 );
}
Esempio n. 6
0
/*
 * Parse a PKCS#1 encoded private RSA key
 */
static int pk_parse_key_pkcs1_der( mbedtls_rsa_context *rsa,
                                   const unsigned char *key,
                                   size_t keylen )
{
    int ret;
    size_t len;
    unsigned char *p, *end;

    p = (unsigned char *) key;
    end = p + keylen;

    /*
     * This function parses the RSAPrivateKey (PKCS#1)
     *
     *  RSAPrivateKey ::= SEQUENCE {
     *      version           Version,
     *      modulus           INTEGER,  -- n
     *      publicExponent    INTEGER,  -- e
     *      privateExponent   INTEGER,  -- d
     *      prime1            INTEGER,  -- p
     *      prime2            INTEGER,  -- q
     *      exponent1         INTEGER,  -- d mod (p-1)
     *      exponent2         INTEGER,  -- d mod (q-1)
     *      coefficient       INTEGER,  -- (inverse of q) mod p
     *      otherPrimeInfos   OtherPrimeInfos OPTIONAL
     *  }
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    end = p + len;

    if( ( ret = mbedtls_asn1_get_int( &p, end, &rsa->ver ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    if( rsa->ver != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_VERSION );
    }

    if( ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->N  ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->E  ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->D  ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->P  ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->Q  ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->DP ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->DQ ) ) != 0 ||
        ( ret = mbedtls_asn1_get_mpi( &p, end, &rsa->QP ) ) != 0 )
    {
        mbedtls_rsa_free( rsa );
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    rsa->len = mbedtls_mpi_size( &rsa->N );

    if( p != end )
    {
        mbedtls_rsa_free( rsa );
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
    }

    if( ( ret = mbedtls_rsa_check_privkey( rsa ) ) != 0 )
    {
        mbedtls_rsa_free( rsa );
        return( ret );
    }

    return( 0 );
}
Esempio n. 7
0
/*
 * Parse a SpecifiedECDomain (SEC 1 C.2) and (mostly) fill the group with it.
 * WARNING: the resulting group should only be used with
 * pk_group_id_from_specified(), since its base point may not be set correctly
 * if it was encoded compressed.
 *
 *  SpecifiedECDomain ::= SEQUENCE {
 *      version SpecifiedECDomainVersion(ecdpVer1 | ecdpVer2 | ecdpVer3, ...),
 *      fieldID FieldID {{FieldTypes}},
 *      curve Curve,
 *      base ECPoint,
 *      order INTEGER,
 *      cofactor INTEGER OPTIONAL,
 *      hash HashAlgorithm OPTIONAL,
 *      ...
 *  }
 *
 * We only support prime-field as field type, and ignore hash and cofactor.
 */
static int pk_group_from_specified( const mbedtls_asn1_buf *params, mbedtls_ecp_group *grp )
{
    int ret;
    unsigned char *p = params->p;
    const unsigned char * const end = params->p + params->len;
    const unsigned char *end_field, *end_curve;
    size_t len;
    int ver;

    /* SpecifiedECDomainVersion ::= INTEGER { 1, 2, 3 } */
    if( ( ret = mbedtls_asn1_get_int( &p, end, &ver ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( ver < 1 || ver > 3 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );

    /*
     * FieldID { FIELD-ID:IOSet } ::= SEQUENCE { -- Finite field
     *       fieldType FIELD-ID.&id({IOSet}),
     *       parameters FIELD-ID.&Type({IOSet}{@fieldType})
     * }
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
        return( ret );

    end_field = p + len;

    /*
     * FIELD-ID ::= TYPE-IDENTIFIER
     * FieldTypes FIELD-ID ::= {
     *       { Prime-p IDENTIFIED BY prime-field } |
     *       { Characteristic-two IDENTIFIED BY characteristic-two-field }
     * }
     * prime-field OBJECT IDENTIFIER ::= { id-fieldType 1 }
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end_field, &len, MBEDTLS_ASN1_OID ) ) != 0 )
        return( ret );

    if( len != MBEDTLS_OID_SIZE( MBEDTLS_OID_ANSI_X9_62_PRIME_FIELD ) ||
        memcmp( p, MBEDTLS_OID_ANSI_X9_62_PRIME_FIELD, len ) != 0 )
    {
        return( MBEDTLS_ERR_PK_FEATURE_UNAVAILABLE );
    }

    p += len;

    /* Prime-p ::= INTEGER -- Field of size p. */
    if( ( ret = mbedtls_asn1_get_mpi( &p, end_field, &grp->P ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    grp->pbits = mbedtls_mpi_bitlen( &grp->P );

    if( p != end_field )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

    /*
     * Curve ::= SEQUENCE {
     *       a FieldElement,
     *       b FieldElement,
     *       seed BIT STRING OPTIONAL
     *       -- Shall be present if used in SpecifiedECDomain
     *       -- with version equal to ecdpVer2 or ecdpVer3
     * }
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
            MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) ) != 0 )
        return( ret );

    end_curve = p + len;

    /*
     * FieldElement ::= OCTET STRING
     * containing an integer in the case of a prime field
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end_curve, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 ||
        ( ret = mbedtls_mpi_read_binary( &grp->A, p, len ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    p += len;

    if( ( ret = mbedtls_asn1_get_tag( &p, end_curve, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 ||
        ( ret = mbedtls_mpi_read_binary( &grp->B, p, len ) ) != 0 )
    {
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );
    }

    p += len;

    /* Ignore seed BIT STRING OPTIONAL */
    if( ( ret = mbedtls_asn1_get_tag( &p, end_curve, &len, MBEDTLS_ASN1_BIT_STRING ) ) == 0 )
        p += len;

    if( p != end_curve )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT +
                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

    /*
     * ECPoint ::= OCTET STRING
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len, MBEDTLS_ASN1_OCTET_STRING ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    if( ( ret = mbedtls_ecp_point_read_binary( grp, &grp->G,
                                      ( const unsigned char *) p, len ) ) != 0 )
    {
        /*
         * If we can't read the point because it's compressed, cheat by
         * reading only the X coordinate and the parity bit of Y.
         */
        if( ret != MBEDTLS_ERR_ECP_FEATURE_UNAVAILABLE ||
            ( p[0] != 0x02 && p[0] != 0x03 ) ||
            len != mbedtls_mpi_size( &grp->P ) + 1 ||
            mbedtls_mpi_read_binary( &grp->G.X, p + 1, len - 1 ) != 0 ||
            mbedtls_mpi_lset( &grp->G.Y, p[0] - 2 ) != 0 ||
            mbedtls_mpi_lset( &grp->G.Z, 1 ) != 0 )
        {
            return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT );
        }
    }

    p += len;

    /*
     * order INTEGER
     */
    if( ( ret = mbedtls_asn1_get_mpi( &p, end, &grp->N ) ) != 0 )
        return( MBEDTLS_ERR_PK_KEY_INVALID_FORMAT + ret );

    grp->nbits = mbedtls_mpi_bitlen( &grp->N );

    /*
     * Allow optional elements by purposefully not enforcing p == end here.
     */

    return( 0 );
}
Esempio n. 8
0
/*
 *    RSASSA-PSS-params  ::=  SEQUENCE  {
 *       hashAlgorithm     [0] HashAlgorithm DEFAULT sha1Identifier,
 *       maskGenAlgorithm  [1] MaskGenAlgorithm DEFAULT mgf1SHA1Identifier,
 *       saltLength        [2] INTEGER DEFAULT 20,
 *       trailerField      [3] INTEGER DEFAULT 1  }
 *    -- Note that the tags in this Sequence are explicit.
 *
 * RFC 4055 (which defines use of RSASSA-PSS in PKIX) states that the value
 * of trailerField MUST be 1, and PKCS#1 v2.2 doesn't even define any other
 * option. Enfore this at parsing time.
 */
int mbedtls_x509_get_rsassa_pss_params( const mbedtls_x509_buf *params,
                                mbedtls_md_type_t *md_alg, mbedtls_md_type_t *mgf_md,
                                int *salt_len )
{
    int ret;
    unsigned char *p;
    const unsigned char *end, *end2;
    size_t len;
    mbedtls_x509_buf alg_id, alg_params;

    /* First set everything to defaults */
    *md_alg = MBEDTLS_MD_SHA1;
    *mgf_md = MBEDTLS_MD_SHA1;
    *salt_len = 20;

    /* Make sure params is a SEQUENCE and setup bounds */
    if( params->tag != ( MBEDTLS_ASN1_CONSTRUCTED | MBEDTLS_ASN1_SEQUENCE ) )
        return( MBEDTLS_ERR_X509_INVALID_ALG +
                MBEDTLS_ERR_ASN1_UNEXPECTED_TAG );

    p = (unsigned char *) params->p;
    end = p + params->len;

    if( p == end )
        return( 0 );

    /*
     * HashAlgorithm
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 0 ) ) == 0 )
    {
        end2 = p + len;

        /* HashAlgorithm ::= AlgorithmIdentifier (without parameters) */
        if( ( ret = mbedtls_x509_get_alg_null( &p, end2, &alg_id ) ) != 0 )
            return( ret );

        if( ( ret = mbedtls_oid_get_md_alg( &alg_id, md_alg ) ) != 0 )
            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

        if( p != end2 )
            return( MBEDTLS_ERR_X509_INVALID_ALG +
                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
    }
    else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

    if( p == end )
        return( 0 );

    /*
     * MaskGenAlgorithm
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 1 ) ) == 0 )
    {
        end2 = p + len;

        /* MaskGenAlgorithm ::= AlgorithmIdentifier (params = HashAlgorithm) */
        if( ( ret = mbedtls_x509_get_alg( &p, end2, &alg_id, &alg_params ) ) != 0 )
            return( ret );

        /* Only MFG1 is recognised for now */
        if( MBEDTLS_OID_CMP( MBEDTLS_OID_MGF1, &alg_id ) != 0 )
            return( MBEDTLS_ERR_X509_FEATURE_UNAVAILABLE +
                    MBEDTLS_ERR_OID_NOT_FOUND );

        /* Parse HashAlgorithm */
        if( ( ret = x509_get_hash_alg( &alg_params, mgf_md ) ) != 0 )
            return( ret );

        if( p != end2 )
            return( MBEDTLS_ERR_X509_INVALID_ALG +
                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
    }
    else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

    if( p == end )
        return( 0 );

    /*
     * salt_len
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 2 ) ) == 0 )
    {
        end2 = p + len;

        if( ( ret = mbedtls_asn1_get_int( &p, end2, salt_len ) ) != 0 )
            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

        if( p != end2 )
            return( MBEDTLS_ERR_X509_INVALID_ALG +
                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
    }
    else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

    if( p == end )
        return( 0 );

    /*
     * trailer_field (if present, must be 1)
     */
    if( ( ret = mbedtls_asn1_get_tag( &p, end, &len,
                    MBEDTLS_ASN1_CONTEXT_SPECIFIC | MBEDTLS_ASN1_CONSTRUCTED | 3 ) ) == 0 )
    {
        int trailer_field;

        end2 = p + len;

        if( ( ret = mbedtls_asn1_get_int( &p, end2, &trailer_field ) ) != 0 )
            return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

        if( p != end2 )
            return( MBEDTLS_ERR_X509_INVALID_ALG +
                    MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

        if( trailer_field != 1 )
            return( MBEDTLS_ERR_X509_INVALID_ALG );
    }
    else if( ret != MBEDTLS_ERR_ASN1_UNEXPECTED_TAG )
        return( MBEDTLS_ERR_X509_INVALID_ALG + ret );

    if( p != end )
        return( MBEDTLS_ERR_X509_INVALID_ALG +
                MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );

    return( 0 );
}