diff --git a/ChangeLog.d/make_base64_table_access_constant_flow.txt b/ChangeLog.d/make_base64_table_access_constant_flow.txt new file mode 100644 index 000000000..733c972d0 --- /dev/null +++ b/ChangeLog.d/make_base64_table_access_constant_flow.txt @@ -0,0 +1,4 @@ +Security + * Guard against strong local side channel attack against base64 tables by + making access aceess to them use constant flow code. + diff --git a/library/base64.c b/library/base64.c index bfafb0535..692e11e3f 100644 --- a/library/base64.c +++ b/library/base64.c @@ -96,6 +96,99 @@ static const unsigned char base64_dec_map[128] = #define BASE64_SIZE_T_MAX ( (size_t) -1 ) /* SIZE_T_MAX is not standard */ +/* + * Constant flow conditional assignment to unsigned char + */ +static void mbedtls_base64_cond_assign_uchar( unsigned char * dest, const unsigned char * const src, + unsigned char condition ) +{ + /* MSVC has a warning about unary minus on unsigned integer types, + * but this is well-defined and precisely what we want to do here. */ +#if defined(_MSC_VER) +#pragma warning( push ) +#pragma warning( disable : 4146 ) +#endif + + /* Generate bitmask from condition, mask will either be 0xFF or 0 */ + unsigned char mask = ( condition | -condition ); + mask >>= 7; + mask = -mask; + +#if defined(_MSC_VER) +#pragma warning( pop ) +#endif + + *dest = ( ( *src ) & mask ) | ( ( *dest ) & ~mask ); +} + +/* + * Constant flow conditional assignment to uint_32 + */ +static void mbedtls_base64_cond_assign_uint32( uint32_t * dest, const uint32_t src, + uint32_t condition ) +{ + /* MSVC has a warning about unary minus on unsigned integer types, + * but this is well-defined and precisely what we want to do here. */ +#if defined(_MSC_VER) +#pragma warning( push ) +#pragma warning( disable : 4146 ) +#endif + + /* Generate bitmask from condition, mask will either be 0xFFFFFFFF or 0 */ + uint32_t mask = ( condition | -condition ); + mask >>= 31; + mask = -mask; + +#if defined(_MSC_VER) +#pragma warning( pop ) +#endif + + *dest = ( src & mask ) | ( ( *dest ) & ~mask ); +} + +/* + * Constant flow check for equality + */ +static unsigned char mbedtls_base64_eq( size_t in_a, size_t in_b ) +{ + size_t difference = in_a ^ in_b; + + /* MSVC has a warning about unary minus on unsigned integer types, + * but this is well-defined and precisely what we want to do here. */ +#if defined(_MSC_VER) +#pragma warning( push ) +#pragma warning( disable : 4146 ) +#endif + + difference |= -difference; + +#if defined(_MSC_VER) +#pragma warning( pop ) +#endif + + /* cope with the varying size of size_t per platform */ + difference >>= ( sizeof( difference ) * 8 - 1 ); + + return (unsigned char) ( 1 ^ difference ); +} + +/* + * Constant flow lookup into table. + */ +static unsigned char mbedtls_base64_table_lookup( const unsigned char * const table, + const size_t table_size, const size_t table_index ) +{ + size_t i; + unsigned char result = 0; + + for( i = 0; i < table_size; ++i ) + { + mbedtls_base64_cond_assign_uchar( &result, &table[i], mbedtls_base64_eq( i, table_index ) ); + } + + return result; +} + /* * Encode a buffer into base64 format */ @@ -136,10 +229,17 @@ int mbedtls_base64_encode( unsigned char *dst, size_t dlen, size_t *olen, C2 = *src++; C3 = *src++; - *p++ = base64_enc_map[(C1 >> 2) & 0x3F]; - *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F]; - *p++ = base64_enc_map[(((C2 & 15) << 2) + (C3 >> 6)) & 0x3F]; - *p++ = base64_enc_map[C3 & 0x3F]; + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( C1 >> 2 ) & 0x3F ) ); + + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( ( ( C1 & 3 ) << 4 ) + ( C2 >> 4 ) ) & 0x3F ) ); + + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( ( ( C2 & 15 ) << 2 ) + ( C3 >> 6 ) ) & 0x3F ) ); + + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( C3 & 0x3F ) ); } if( i < slen ) @@ -147,11 +247,15 @@ int mbedtls_base64_encode( unsigned char *dst, size_t dlen, size_t *olen, C1 = *src++; C2 = ( ( i + 1 ) < slen ) ? *src++ : 0; - *p++ = base64_enc_map[(C1 >> 2) & 0x3F]; - *p++ = base64_enc_map[(((C1 & 3) << 4) + (C2 >> 4)) & 0x3F]; + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( C1 >> 2 ) & 0x3F ) ); + + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( ( ( C1 & 3 ) << 4 ) + ( C2 >> 4 ) ) & 0x3F ) ); if( ( i + 1 ) < slen ) - *p++ = base64_enc_map[((C2 & 15) << 2) & 0x3F]; + *p++ = mbedtls_base64_table_lookup( base64_enc_map, sizeof( base64_enc_map ), + ( ( ( C2 & 15 ) << 2 ) & 0x3F ) ); else *p++ = '='; *p++ = '='; @@ -172,6 +276,7 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen, size_t i, n; uint32_t j, x; unsigned char *p; + unsigned char dec_map_lookup; /* First pass: check for validity and get output length */ for( i = n = j = 0; i < slen; i++ ) @@ -202,10 +307,12 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen, if( src[i] == '=' && ++j > 2 ) return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); - if( src[i] > 127 || base64_dec_map[src[i]] == 127 ) + dec_map_lookup = mbedtls_base64_table_lookup( base64_dec_map, sizeof( base64_dec_map ), src[i] ); + + if( src[i] > 127 || dec_map_lookup == 127 ) return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); - if( base64_dec_map[src[i]] < 64 && j != 0 ) + if( dec_map_lookup < 64 && j != 0 ) return( MBEDTLS_ERR_BASE64_INVALID_CHARACTER ); n++; @@ -235,8 +342,10 @@ int mbedtls_base64_decode( unsigned char *dst, size_t dlen, size_t *olen, if( *src == '\r' || *src == '\n' || *src == ' ' ) continue; - j -= ( base64_dec_map[*src] == 64 ); - x = ( x << 6 ) | ( base64_dec_map[*src] & 0x3F ); + dec_map_lookup = mbedtls_base64_table_lookup( base64_dec_map, sizeof( base64_dec_map ), *src ); + + mbedtls_base64_cond_assign_uint32( &j, j - 1, mbedtls_base64_eq( dec_map_lookup, 64 ) ); + x = ( x << 6 ) | ( dec_map_lookup & 0x3F ); if( ++n == 4 ) { diff --git a/tests/suites/test_suite_base64.data b/tests/suites/test_suite_base64.data index da99ffa87..3a892f479 100644 --- a/tests/suites/test_suite_base64.data +++ b/tests/suites/test_suite_base64.data @@ -151,6 +151,20 @@ base64_encode_hex:"0102030405060708":"AQIDBAUGBwg=":13:0 Base64 encode hex #4 base64_encode_hex:"01020304050607":"AQIDBAUGBw==":13:0 +# Rotate the bytes around so that they end up at each offset modulo 3 in +# successive test cases. +Base64 encode hex all valid input bytes #0 +base64_encode_hex:"000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff":"AAECAwQFBgcICQoLDA0ODxAREhMUFRYXGBkaGxwdHh8gISIjJCUmJygpKissLS4vMDEyMzQ1Njc4OTo7PD0+P0BBQkNERUZHSElKS0xNTk9QUVJTVFVWV1hZWltcXV5fYGFiY2RlZmdoaWprbG1ub3BxcnN0dXZ3eHl6e3x9fn+AgYKDhIWGh4iJiouMjY6PkJGSk5SVlpeYmZqbnJ2en6ChoqOkpaanqKmqq6ytrq+wsbKztLW2t7i5uru8vb6/wMHCw8TFxsfIycrLzM3Oz9DR0tPU1dbX2Nna29zd3t/g4eLj5OXm5+jp6uvs7e7v8PHy8/T19vf4+fr7/P3+/w==":345:0 + +Base64 encode hex all valid input bytes #1 +base64_encode_hex:"0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff00":"AQIDBAUGBwgJCgsMDQ4PEBESExQVFhcYGRobHB0eHyAhIiMkJSYnKCkqKywtLi8wMTIzNDU2Nzg5Ojs8PT4/QEFCQ0RFRkdISUpLTE1OT1BRUlNUVVZXWFlaW1xdXl9gYWJjZGVmZ2hpamtsbW5vcHFyc3R1dnd4eXp7fH1+f4CBgoOEhYaHiImKi4yNjo+QkZKTlJWWl5iZmpucnZ6foKGio6SlpqeoqaqrrK2ur7CxsrO0tba3uLm6u7y9vr/AwcLDxMXGx8jJysvMzc7P0NHS09TV1tfY2drb3N3e3+Dh4uPk5ebn6Onq6+zt7u/w8fLz9PX29/j5+vv8/f7/AA==":345:0 + +Base64 encode hex all valid input bytes #2 +base64_encode_hex:"02030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132333435363738393a3b3c3d3e3f404142434445464748494a4b4c4d4e4f505152535455565758595a5b5c5d5e5f606162636465666768696a6b6c6d6e6f707172737475767778797a7b7c7d7e7f808182838485868788898a8b8c8d8e8f909192939495969798999a9b9c9d9e9fa0a1a2a3a4a5a6a7a8a9aaabacadaeafb0b1b2b3b4b5b6b7b8b9babbbcbdbebfc0c1c2c3c4c5c6c7c8c9cacbcccdcecfd0d1d2d3d4d5d6d7d8d9dadbdcdddedfe0e1e2e3e4e5e6e7e8e9eaebecedeeeff0f1f2f3f4f5f6f7f8f9fafbfcfdfeff0001":"AgMEBQYHCAkKCwwNDg8QERITFBUWFxgZGhscHR4fICEiIyQlJicoKSorLC0uLzAxMjM0NTY3ODk6Ozw9Pj9AQUJDREVGR0hJSktMTU5PUFFSU1RVVldYWVpbXF1eX2BhYmNkZWZnaGlqa2xtbm9wcXJzdHV2d3h5ent8fX5/gIGCg4SFhoeIiYqLjI2Oj5CRkpOUlZaXmJmam5ydnp+goaKjpKWmp6ipqqusra6vsLGys7S1tre4ubq7vL2+v8DBwsPExcbHyMnKy8zNzs/Q0dLT1NXW19jZ2tvc3d7f4OHi4+Tl5ufo6err7O3u7/Dx8vP09fb3+Pn6+/z9/v8AAQ==":345:0 + +Base64 encode all valid output characters at all offsets +base64_encode_hex:"00108310518720928b30d38f41149351559761969b71d79f8218a39259a7a29aabb2dbafc31cb3d35db7e39ebbf3dfbff800420c41461c824a2cc34e3d04524d45565d865a6dc75e7e08628e49669e8a6aaecb6ebf0c72cf4d76df8e7aefcf7effe00108310518720928b30d38f41149351559761969b71d79f8218a39259a7a29aabb2dbafc31cb3d35db7e39ebbf3dfbff800420c41461c824a2cc34e3d04524d45565d865a6dc75e7e08628e49669e8a6aaecb6ebf0c72cf4d76df8e7aefcf7efd0":"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/Q":261:0 + Base64 decode hex #1 base64_decode_hex:"AQIDBAUGBwgJ":"010203040506070809":9:0 @@ -166,6 +180,9 @@ base64_decode_hex:"AQIDBAUGBw==":"01020304050607":7:0 Base64 decode hex #5 (buffer too small) base64_decode_hex:"AQIDBAUGBw==":"01020304050607":6:MBEDTLS_ERR_BASE64_BUFFER_TOO_SMALL +Base64 decode all valid input characters at all offsets +base64_decode_hex:"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/+ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/Q":"00108310518720928b30d38f41149351559761969b71d79f8218a39259a7a29aabb2dbafc31cb3d35db7e39ebbf3dfbff800420c41461c824a2cc34e3d04524d45565d865a6dc75e7e08628e49669e8a6aaecb6ebf0c72cf4d76df8e7aefcf7effe00108310518720928b30d38f41149351559761969b71d79f8218a39259a7a29aabb2dbafc31cb3d35db7e39ebbf3dfbff800420c41461c824a2cc34e3d04524d45565d865a6dc75e7e08628e49669e8a6aaecb6ebf0c72cf4d76df8e7aefcf7efd0":195:0 + Base64 Selftest depends_on:MBEDTLS_SELF_TEST base64_selftest: diff --git a/tests/suites/test_suite_base64.function b/tests/suites/test_suite_base64.function index 3a8bf430f..0185f3b24 100644 --- a/tests/suites/test_suite_base64.function +++ b/tests/suites/test_suite_base64.function @@ -13,13 +13,22 @@ void mbedtls_base64_encode( char * src_string, char * dst_string, { unsigned char src_str[1000]; unsigned char dst_str[1000]; - size_t len; + size_t len, src_len; memset(src_str, 0x00, 1000); memset(dst_str, 0x00, 1000); strncpy( (char *) src_str, src_string, sizeof(src_str) - 1 ); - TEST_ASSERT( mbedtls_base64_encode( dst_str, dst_buf_size, &len, src_str, strlen( (char *) src_str ) ) == result ); + src_len = strlen( (char *) src_str ); + + TEST_CF_SECRET( src_str, sizeof( src_str ) ); + TEST_ASSERT( mbedtls_base64_encode( dst_str, dst_buf_size, &len, src_str, src_len) == result ); + TEST_CF_PUBLIC( src_str, sizeof( src_str ) ); + + /* dest_str will have had tainted data copied to it, prevent the TEST_ASSERT below from triggering + CF failures by unmarking it. */ + TEST_CF_PUBLIC( dst_str, len ); + if( result == 0 ) { TEST_ASSERT( strcmp( (char *) dst_str, dst_string ) == 0 ); @@ -57,7 +66,14 @@ void base64_encode_hex( data_t * src, char * dst, int dst_buf_size, res = zero_alloc( dst_buf_size ); + TEST_CF_SECRET( src->x, src->len ); TEST_ASSERT( mbedtls_base64_encode( res, dst_buf_size, &len, src->x, src->len ) == result ); + TEST_CF_PUBLIC( src->x, src->len ); + + /* res will have had tainted data copied to it, prevent the TEST_ASSERT below from triggering + CF failures by unmarking it. */ + TEST_CF_PUBLIC( res, len ); + if( result == 0 ) { TEST_ASSERT( len == strlen( dst ) );