Improve and augment export sanity checks
Implement sanity checks of exported public keys, using ASN.1 parsing. Rewrite the sanity checks of key pairs using ASN.1 parsing, so as to check more things with simpler code.
This commit is contained in:
Gilles Peskine
Jaeden Amero
parent
cb6adbb750
commit
dd2f95b855
1 changed files with 269 additions and 54 deletions
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@ -5,7 +5,10 @@
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#include "spm/psa_defs.h"
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#endif
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#include "mbedtls/asn1.h"
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#include "mbedtls/asn1write.h"
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#include "mbedtls/oid.h"
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#include "psa/crypto.h"
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#define ARRAY_LENGTH( array ) ( sizeof( array ) / sizeof( *( array ) ) )
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@ -38,13 +41,6 @@ static int mem_is_zero( void *buffer, size_t size )
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return( 1 );
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}
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static int key_type_is_raw_bytes( psa_key_type_t type )
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{
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psa_key_type_t category = type & PSA_KEY_TYPE_CATEGORY_MASK;
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return( category == PSA_KEY_TYPE_RAW_DATA ||
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category == PSA_KEY_TYPE_CATEGORY_SYMMETRIC );
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}
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/* Write the ASN.1 INTEGER with the value 2^(bits-1)+x backwards from *p. */
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static int asn1_write_10x( unsigned char **p,
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unsigned char *start,
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@ -393,11 +389,118 @@ exit:
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return( 0 );
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}
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int exported_key_sanity_check( psa_key_type_t type, size_t bits,
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typedef struct
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{
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unsigned char length;
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unsigned char string[];
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} small_byte_string_t;
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#define DECLARE_SMALL_STRING_OF_LITERAL( name, literal ) \
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static const small_byte_string_t name = \
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{ sizeof( literal ) - 1, literal }
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#if defined(MBEDTLS_RSA_C)
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DECLARE_SMALL_STRING_OF_LITERAL( key_type_oid_rsa,
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MBEDTLS_OID_PKCS1_RSA );
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#endif
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#if defined(MBEDTLS_ECP_C)
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DECLARE_SMALL_STRING_OF_LITERAL( key_type_oid_ecc,
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MBEDTLS_OID_EC_ALG_UNRESTRICTED );
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#endif
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static int is_oid_of_key_type( psa_key_type_t type,
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const uint8_t *oid, size_t oid_length )
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{
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const small_byte_string_t *expected_oid =
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#if defined(MBEDTLS_RSA_C)
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PSA_KEY_TYPE_IS_RSA( type ) ? &key_type_oid_rsa :
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#endif /* MBEDTLS_RSA_C */
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#if defined(MBEDTLS_ECP_C)
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PSA_KEY_TYPE_IS_ECC( type ) ? &key_type_oid_ecc :
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#endif /* MBEDTLS_ECP_C */
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NULL;
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if( expected_oid == NULL )
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{
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char message[40];
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mbedtls_snprintf( message, sizeof( message ),
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"OID not known for key type=0x%08lx",
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(unsigned long) type );
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test_fail( message, __LINE__, __FILE__ );
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return( 0 );
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}
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TEST_ASSERT( oid_length == expected_oid->length );
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TEST_ASSERT( memcmp( oid, expected_oid->string, oid_length ) == 0 );
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return( 1 );
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exit:
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return( 0 );
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}
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static int asn1_skip_integer( unsigned char **p, const unsigned char *end,
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size_t min_bits, size_t max_bits,
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int must_be_odd )
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{
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size_t len;
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size_t actual_bits;
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unsigned char msb;
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TEST_ASSERT( mbedtls_asn1_get_tag( p, end, &len,
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MBEDTLS_ASN1_INTEGER ) == 0 );
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/* Tolerate a slight departure from DER encoding:
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* - 0 may be represented by an empty string or a 1-byte string.
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* - The sign bit may be used as a value bit. */
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if( ( len == 1 && ( *p )[0] == 0 ) ||
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( len > 1 && ( *p )[0] == 0 && ( ( *p )[1] & 0x80 ) != 0 ) )
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{
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++( *p );
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--len;
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}
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if( min_bits == 0 && len == 0 )
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return( 1 );
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msb = ( *p )[0];
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TEST_ASSERT( msb != 0 );
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actual_bits = 8 * ( len - 1 );
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while( msb != 0 )
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{
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msb >>= 1;
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++actual_bits;
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}
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TEST_ASSERT( actual_bits >= min_bits );
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TEST_ASSERT( actual_bits <= max_bits );
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if( must_be_odd )
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TEST_ASSERT( ( ( *p )[len-1] & 1 ) != 0 );
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*p += len;
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return( 1 );
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exit:
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return( 0 );
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}
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static int asn1_get_implicit_tag( unsigned char **p, const unsigned char *end,
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size_t *len,
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unsigned char n, unsigned char tag )
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{
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int ret;
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ret = mbedtls_asn1_get_tag( p, end, len,
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MBEDTLS_ASN1_CONTEXT_SPECIFIC |
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MBEDTLS_ASN1_CONSTRUCTED | ( n ) );
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if( ret != 0 )
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return( ret );
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end = *p + *len;
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ret = mbedtls_asn1_get_tag( p, end, len, tag );
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if( ret != 0 )
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return( ret );
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if( *p + *len != end )
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return( MBEDTLS_ERR_ASN1_LENGTH_MISMATCH );
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return( 0 );
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}
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static int exported_key_sanity_check( psa_key_type_t type, size_t bits,
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uint8_t *exported, size_t exported_length )
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{
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if( key_type_is_raw_bytes( type ) )
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if( PSA_KEY_TYPE_IS_UNSTRUCTURED( type ) )
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TEST_ASSERT( exported_length == ( bits + 7 ) / 8 );
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else
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TEST_ASSERT( exported_length <= PSA_KEY_EXPORT_MAX_SIZE( type, bits ) );
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#if defined(MBEDTLS_DES_C)
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if( type == PSA_KEY_TYPE_DES )
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@ -416,64 +519,176 @@ int exported_key_sanity_check( psa_key_type_t type, size_t bits,
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TEST_ASSERT( bit_count % 2 != 0 );
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}
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}
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else
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#endif
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#if defined(MBEDTLS_RSA_C) && defined(MBEDTLS_PK_PARSE_C)
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if( type == PSA_KEY_TYPE_RSA_KEYPAIR )
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{
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/* Sanity check: does this look like the beginning of a PKCS#8
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* RSA key pair? Assumes bits is a multiple of 8. */
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size_t n_bytes = bits / 8 + 1;
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size_t n_encoded_bytes;
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unsigned char *n_end;
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TEST_ASSERT( exported_length >= 7 + ( n_bytes + 3 ) * 9 / 2 );
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TEST_ASSERT( exported[0] == 0x30 );
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TEST_ASSERT( exported[1] == 0x82 ); // assumes >=416-bit key
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TEST_ASSERT( exported[4] == 0x02 );
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TEST_ASSERT( exported[5] == 0x01 );
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TEST_ASSERT( exported[6] == 0x00 );
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TEST_ASSERT( exported[7] == 0x02 );
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n_encoded_bytes = exported[8];
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n_end = exported + 9 + n_encoded_bytes;
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if( n_encoded_bytes & 0x80 )
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{
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n_encoded_bytes = ( n_encoded_bytes & 0x7f ) << 7;
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n_encoded_bytes |= exported[9] & 0x7f;
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n_end += 1;
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}
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/* The encoding of n should start with a 0 byte since it should
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* have its high bit set. However Mbed TLS is not compliant and
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* generates an invalid, but widely tolerated, encoding of
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* positive INTEGERs with a bit size that is a multiple of 8
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* with no leading 0 byte. Accept this here. */
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TEST_ASSERT( n_bytes == n_encoded_bytes ||
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n_bytes == n_encoded_bytes + 1 );
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if( n_bytes == n_encoded_bytes )
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TEST_ASSERT( exported[n_encoded_bytes <= 127 ? 9 : 10] == 0x00 );
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/* Sanity check: e must be 3 */
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TEST_ASSERT( n_end[0] == 0x02 );
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TEST_ASSERT( n_end[1] == 0x03 );
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TEST_ASSERT( n_end[2] == 0x01 );
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TEST_ASSERT( n_end[3] == 0x00 );
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TEST_ASSERT( n_end[4] == 0x01 );
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TEST_ASSERT( n_end[5] == 0x02 );
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uint8_t *p = exported;
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uint8_t *end = exported + exported_length;
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size_t len;
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/* RSAPrivateKey ::= SEQUENCE {
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* version Version, -- 0
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* modulus INTEGER, -- n
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* publicExponent INTEGER, -- e
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* privateExponent INTEGER, -- d
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* prime1 INTEGER, -- p
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* prime2 INTEGER, -- q
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* exponent1 INTEGER, -- d mod (p-1)
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* exponent2 INTEGER, -- d mod (q-1)
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* coefficient INTEGER, -- (inverse of q) mod p
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* }
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*/
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TEST_ASSERT( mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_SEQUENCE |
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MBEDTLS_ASN1_CONSTRUCTED ) == 0 );
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TEST_ASSERT( p + len == end );
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if( ! asn1_skip_integer( &p, end, 0, 0, 0 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, bits, bits, 1 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, 2, bits, 1 ) )
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goto exit;
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/* Require d to be at least half the size of n. */
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if( ! asn1_skip_integer( &p, end, bits / 2, bits, 1 ) )
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goto exit;
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/* Require p and q to be at most half the size of n, rounded up. */
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if( ! asn1_skip_integer( &p, end, bits / 2, bits / 2 + 1, 1 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, bits / 2, bits / 2 + 1, 1 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, 1, bits / 2 + 1, 0 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, 1, bits / 2 + 1, 0 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, 1, bits / 2 + 1, 0 ) )
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goto exit;
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TEST_ASSERT( p == end );
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}
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else
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#endif /* MBEDTLS_RSA_C */
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#if defined(MBEDTLS_ECP_C)
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if( PSA_KEY_TYPE_IS_ECC_KEYPAIR( type ) )
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{
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/* Sanity check: does this look like the beginning of a PKCS#8
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* elliptic curve key pair? */
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TEST_ASSERT( exported_length >= bits * 3 / 8 + 10 );
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TEST_ASSERT( exported[0] == 0x30 );
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uint8_t *p = exported;
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uint8_t *end = exported + exported_length;
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size_t len;
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int version;
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/* ECPrivateKey ::= SEQUENCE {
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* version INTEGER, -- must be 1
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* privateKey OCTET STRING,
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* -- `ceiling(log_{256}(n))`-byte string, big endian,
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* -- where n is the order of the curve.
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* parameters ECParameters {{ NamedCurve }}, -- mandatory
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* publicKey BIT STRING -- mandatory
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* }
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*/
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TEST_ASSERT( mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_SEQUENCE |
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MBEDTLS_ASN1_CONSTRUCTED ) == 0 );
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TEST_ASSERT( p + len == end );
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TEST_ASSERT( mbedtls_asn1_get_int( &p, end, &version ) == 0 );
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TEST_ASSERT( version == 1 );
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TEST_ASSERT( mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_OCTET_STRING ) == 0 );
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/* Bug in Mbed TLS: the length of the octet string depends on the value */
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// TEST_ASSERT( len == PSA_BITS_TO_BYTES( bits ) );
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p += len;
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TEST_ASSERT( asn1_get_implicit_tag( &p, end, &len, 0,
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MBEDTLS_ASN1_OID ) == 0 );
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p += len;
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TEST_ASSERT( asn1_get_implicit_tag( &p, end, &len, 1,
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MBEDTLS_ASN1_BIT_STRING ) == 0 );
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TEST_ASSERT( p + len == end );
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TEST_ASSERT( p[0] == 0 ); /* 0 unused bits in the bit string */
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++p;
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TEST_ASSERT( p + 1 + 2 * PSA_BITS_TO_BYTES( bits ) == end );
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TEST_ASSERT( p[0] == 4 );
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}
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else
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#endif /* MBEDTLS_ECP_C */
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if( PSA_KEY_TYPE_IS_PUBLIC_KEY( type ) )
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{
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uint8_t *p = exported;
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uint8_t *end = exported + exported_length;
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size_t len;
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mbedtls_asn1_buf alg;
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mbedtls_asn1_buf params;
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mbedtls_asn1_bitstring bitstring;
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/* SubjectPublicKeyInfo ::= SEQUENCE {
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* algorithm AlgorithmIdentifier,
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* subjectPublicKey BIT STRING }
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* AlgorithmIdentifier ::= SEQUENCE {
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* algorithm OBJECT IDENTIFIER,
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* parameters ANY DEFINED BY algorithm OPTIONAL }
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*/
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TEST_ASSERT( mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_SEQUENCE |
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MBEDTLS_ASN1_CONSTRUCTED ) == 0 );
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TEST_ASSERT( p + len == end );
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TEST_ASSERT( mbedtls_asn1_get_alg( &p, end, &alg, ¶ms ) == 0 );
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if( ! is_oid_of_key_type( type, alg.p, alg.len ) )
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goto exit;
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TEST_ASSERT( mbedtls_asn1_get_bitstring( &p, end, &bitstring ) == 0 );
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TEST_ASSERT( p == end );
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p = bitstring.p;
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#if defined(MBEDTLS_RSA_C)
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if( type == PSA_KEY_TYPE_RSA_PUBLIC_KEY )
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{
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/* RSAPublicKey ::= SEQUENCE {
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* modulus INTEGER, -- n
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* publicExponent INTEGER } -- e
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*/
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TEST_ASSERT( bitstring.unused_bits == 0 );
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TEST_ASSERT( mbedtls_asn1_get_tag( &p, end, &len,
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MBEDTLS_ASN1_SEQUENCE |
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MBEDTLS_ASN1_CONSTRUCTED ) == 0 );
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TEST_ASSERT( p + len == end );
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if( ! asn1_skip_integer( &p, end, bits, bits, 1 ) )
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goto exit;
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if( ! asn1_skip_integer( &p, end, 2, bits, 1 ) )
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goto exit;
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TEST_ASSERT( p == end );
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}
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else
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#endif /* MBEDTLS_RSA_C */
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#if defined(MBEDTLS_ECP_C)
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if( PSA_KEY_TYPE_IS_ECC_PUBLIC_KEY( type ) )
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{
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/* ECPoint ::= ...
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* -- first 8 bits: 0x04;
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* -- then x_P as an n-bit string, big endian;
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* -- then y_P as a n-bit string, big endian,
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* -- where n is the order of the curve.
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*/
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TEST_ASSERT( bitstring.unused_bits == 0 );
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TEST_ASSERT( p + 1 + 2 * PSA_BITS_TO_BYTES( bits ) == end );
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TEST_ASSERT( p[0] == 4 );
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}
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else
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#endif /* MBEDTLS_ECP_C */
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{
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char message[40];
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mbedtls_snprintf( message, sizeof( message ),
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"No sanity check for public key type=0x%08lx",
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(unsigned long) type );
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test_fail( message, __LINE__, __FILE__ );
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return( 0 );
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}
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}
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else
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{
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/* No sanity checks for other types */
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}
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return( 1 );
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exit:
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return( 1 );
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return( 0 );
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}
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static int exercise_export_key( psa_key_slot_t slot,
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