commit f931d6e47bf2fb26aa9cf52e231d13edc1c837a1 Author: Ingo Franzki Date: Tue Dec 12 17:16:56 2023 +0100 COMMON: Update rsa_parse_block_type_2() to not leak the message length Take the implementation of OpenSSL function RSA_padding_check_PKCS1_type_2() in crypto/rsa/rsa_pk1.c instead of ossl_rsa_padding_check_PKCS1_type_2(), since the latter leaks the message size. Signed-off-by: Ingo Franzki diff --git a/usr/lib/common/mech_rsa.c b/usr/lib/common/mech_rsa.c index 326c5795..7bab1a84 100644 --- a/usr/lib/common/mech_rsa.c +++ b/usr/lib/common/mech_rsa.c @@ -29,6 +29,7 @@ #include "constant_time.h" #include +#include CK_BBOOL is_rsa_mechanism(CK_MECHANISM_TYPE mech) { @@ -293,13 +294,16 @@ static CK_RV rsa_parse_block_type_2(CK_BYTE *in_data, CK_BYTE *out_data, CK_ULONG *out_data_len) { - unsigned int ok = 0, found, zero; - size_t zero_index = 0, msg_index, mlen; - size_t i, j; + int i; + unsigned char *em = NULL; + unsigned int good, found_zero_byte, mask, equals0; + int zero_index = 0, msg_index, mlen = -1; + int out_len = *out_data_len; + int rsa_size = in_data_len; /* * The implementation of this function is copied from OpenSSL's function - * ossl_rsa_padding_check_PKCS1_type_2() in crypto/rsa/rsa_pk1.c + * RSA_padding_check_PKCS1_type_2() in crypto/rsa/rsa_pk1.c * and is slightly modified to fit to the OpenCryptoki environment. * * The OpenSSL code is licensed under the Apache License 2.0. @@ -324,55 +328,86 @@ static CK_RV rsa_parse_block_type_2(CK_BYTE *in_data, * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard", * section 7.2.2. */ - if (in_data_len < 11) { + if (rsa_size < RSA_PKCS1_PADDING_SIZE) { TRACE_DEVEL("%s\n", ock_err(ERR_FUNCTION_FAILED)); return CKR_FUNCTION_FAILED; } - ok = constant_time_is_zero(in_data[0]); - ok &= constant_time_eq(in_data[1], 2); + em = malloc(rsa_size); + if (em == NULL) { + TRACE_DEVEL("%s\n", ock_err(ERR_HOST_MEMORY)); + return CKR_HOST_MEMORY; + } + + /* in_data_len is always equal to rsa_size */ + memcpy(em, in_data, rsa_size); + + good = constant_time_is_zero(em[0]); + good &= constant_time_eq(em[1], 2); /* scan over padding data */ - found = 0; - for (i = 2; i < in_data_len; i++) { - zero = constant_time_is_zero(in_data[i]); + found_zero_byte = 0; + for (i = 2; i < rsa_size; i++) { + equals0 = constant_time_is_zero(em[i]); - zero_index = constant_time_select_int(~found & zero, i, zero_index); - found |= zero; + zero_index = constant_time_select_int(~found_zero_byte & equals0, + i, zero_index); + found_zero_byte |= equals0; } /* - * PS must be at least 8 bytes long, and it starts two bytes into |enc_msg|. + * PS must be at least 8 bytes long, and it starts two bytes into |em|. * If we never found a 0-byte, then |zero_index| is 0 and the check * also fails. */ - ok &= constant_time_ge(zero_index, 2 + 8); + good &= constant_time_ge(zero_index, 2 + 8); /* * Skip the zero byte. This is incorrect if we never found a zero-byte * but in this case we also do not copy the message out. */ msg_index = zero_index + 1; - mlen = in_data_len - msg_index; + mlen = rsa_size - msg_index; /* * For good measure, do this check in constant time as well. */ - ok &= constant_time_ge(*out_data_len, mlen); + good &= constant_time_ge(out_len, mlen); /* - * since at this point the |msg_index| does not provide the signal - * indicating if the padding check failed or not, we don't have to worry - * about leaking the length of returned message, we still need to ensure - * that we read contents of both buffers so that cache accesses don't leak - * the value of |good| + * Move the result in-place by |rsa_size|-RSA_PKCS1_PADDING_SIZE-|mlen| + * bytes to the left. + * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to + * |out_data|. Otherwise leave |out_data| unchanged. + * Copy the memory back in a way that does not reveal the size of + * the data being copied via a timing side channel. This requires copying + * parts of the buffer multiple times based on the bits set in the real + * length. Clear bits do a non-copy with identical access pattern. + * The loop below has overall complexity of O(N*log(N)). */ - for (i = msg_index, j = 0; i < in_data_len && j < *out_data_len; i++, j++) - out_data[j] = constant_time_select_8(ok, in_data[i], out_data[j]); + out_len = constant_time_select_int( + constant_time_lt(rsa_size - RSA_PKCS1_PADDING_SIZE, out_len), + rsa_size - RSA_PKCS1_PADDING_SIZE, + out_len); + for (msg_index = 1; msg_index < rsa_size - RSA_PKCS1_PADDING_SIZE; + msg_index <<= 1) { + mask = ~constant_time_eq( + msg_index & (rsa_size - RSA_PKCS1_PADDING_SIZE - mlen), 0); + for (i = RSA_PKCS1_PADDING_SIZE; i < rsa_size - msg_index; i++) + em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]); + } + for (i = 0; i < out_len; i++) { + mask = good & constant_time_lt(i, mlen); + out_data[i] = constant_time_select_8( + mask, em[i + RSA_PKCS1_PADDING_SIZE], out_data[i]); + } + + OPENSSL_cleanse(em, rsa_size); + free(em); - *out_data_len = j; + *out_data_len = constant_time_select_int(good, mlen, 0); - return constant_time_select_int(ok, CKR_OK, CKR_ENCRYPTED_DATA_INVALID); + return constant_time_select_int(good, CKR_OK, CKR_ENCRYPTED_DATA_INVALID); } CK_RV rsa_parse_block(CK_BYTE *in_data,