diff --git a/components/mbedtls/port/psa_driver/esp_rsa_ds/psa_crypto_driver_esp_rsa_ds_utilities.c b/components/mbedtls/port/psa_driver/esp_rsa_ds/psa_crypto_driver_esp_rsa_ds_utilities.c index 1a491bcc004..fc19cfce2c3 100644 --- a/components/mbedtls/port/psa_driver/esp_rsa_ds/psa_crypto_driver_esp_rsa_ds_utilities.c +++ b/components/mbedtls/port/psa_driver/esp_rsa_ds/psa_crypto_driver_esp_rsa_ds_utilities.c @@ -9,9 +9,7 @@ #include "mbedtls/asn1.h" #include "mbedtls/psa_util.h" #include "esp_log.h" -/* The unpadding routines below borrow the audited constant-time primitives - * from upstream mbedtls (the same header is already used by the esp_aes - * driver in this tree). */ +#include "mbedtls/constant_time.h" #include "constant_time_internal.h" typedef struct { @@ -449,81 +447,91 @@ psa_status_t esp_rsa_ds_pad_oaep_unpad(unsigned char *input, size_t *olen, psa_algorithm_t hash_alg) { + /* This mirrors mbedtls_rsa_rsaes_oaep_decrypt() in upstream rsa.c. + * Below the public-input sanity check, the unpadding scan operates + * only through mbedtls_ct primitives, so its time and memory trace + * depend solely on ilen and hash_alg. The single branch on `bad` + * at the end leaks no more than the return value already does, + * which matches the upstream design and is acceptable for OAEP + * (the relevant side-channel attack relies on distinguishing + * failure modes, not on timing the success path). */ + unsigned int hlen = PSA_HASH_LENGTH(hash_alg); - unsigned char bad = 0; - size_t msg_len = 0; - - /* Validate input length */ - bad |= (ilen < 2 * hlen + 2); - - /* Apply MGF masks */ - bad |= esp_rsa_ds_mgf_mask(input + 1, hlen, input + hlen + 1, ilen - hlen - 1, hash_alg) != PSA_SUCCESS; - - bad |= esp_rsa_ds_mgf_mask(input + hlen + 1, ilen - hlen - 1, input + 1, hlen, hash_alg) != PSA_SUCCESS; - - /* Check first byte (should be 0x00) */ - bad |= input[0]; - - /* Skip the first byte and maskSeed */ - unsigned char *db = input + 1 + hlen; - size_t db_len = ilen - hlen - 1; - - /* Compute hash, label is NULL and label_len is 0 */ + mbedtls_ct_condition_t bad; + mbedtls_ct_condition_t in_padding; + size_t pad_len; + unsigned char *p; unsigned char lhash[PSA_HASH_MAX_SIZE]; - memset(lhash, 0, sizeof(lhash)); + + /* All lengths checked here are public. */ + if (hlen == 0 || hlen > PSA_HASH_MAX_SIZE || ilen < 2 * hlen + 2) { + return PSA_ERROR_INVALID_ARGUMENT; + } + + /* Unmask seed and DB. A failure here is an internal hash error, + * not a ciphertext-dependent condition, so an early return is + * safe. */ + if (esp_rsa_ds_mgf_mask(input + 1, hlen, + input + hlen + 1, ilen - hlen - 1, hash_alg) != PSA_SUCCESS || + esp_rsa_ds_mgf_mask(input + hlen + 1, ilen - hlen - 1, + input + 1, hlen, hash_alg) != PSA_SUCCESS) { + return PSA_ERROR_INVALID_ARGUMENT; + } + + /* lHash of the empty label, recomputed each call. */ size_t lhen = 0; - bad |= psa_hash_compute(hash_alg, NULL, 0, lhash, sizeof(lhash), &lhen) != PSA_SUCCESS; - - bad |= (lhen != hlen); - - /* Verify hash portion of db against lhash */ - for (size_t i = 0; i < hlen && i < db_len; i++) { - bad |= db[i] ^ lhash[i]; + if (psa_hash_compute(hash_alg, NULL, 0, lhash, sizeof(lhash), &lhen) != PSA_SUCCESS + || lhen != hlen) { + mbedtls_platform_zeroize(lhash, sizeof(lhash)); + return PSA_ERROR_INVALID_ARGUMENT; } - /* Skip past lhash in DB */ - unsigned char *p = db + hlen; - size_t remaining = db_len - hlen; + /* Constant-time padding check. */ + p = input; + bad = mbedtls_ct_bool(*p++); /* First byte must be 0x00 */ + p += hlen; /* Skip seed */ + bad = mbedtls_ct_bool_or(bad, + mbedtls_ct_bool(mbedtls_ct_memcmp(lhash, p, hlen))); + p += hlen; - /* - * Scan PS || 0x01 || M - */ - unsigned char seen_one = 0; - size_t msg_index = 0; - - for (size_t i = 0; i < remaining; i++) { - unsigned char is_zero = (p[i] == 0); - unsigned char is_one = (p[i] == 1); - - /* Before delimiter, only 0x00 allowed */ - bad |= (seen_one == 0) & !(is_zero | is_one); - - /* Record first 0x01 */ - msg_index |= (seen_one == 0 && is_one) * i; - seen_one |= is_one; + /* Count leading zeros in DB (between lHash and the 0x01 delimiter). + * The loop scans the full DB region every time; the latch via + * in_padding keeps pad_len from incrementing once a non-zero byte + * is seen. */ + pad_len = 0; + in_padding = MBEDTLS_CT_TRUE; + for (size_t i = 0; i < ilen - 2 * hlen - 2; i++) { + in_padding = mbedtls_ct_bool_and(in_padding, mbedtls_ct_uint_eq(p[i], 0)); + pad_len += mbedtls_ct_uint_if_else_0(in_padding, 1); } + p += pad_len; + bad = mbedtls_ct_bool_or(bad, mbedtls_ct_uint_ne(*p++, 0x01)); - /* Must see exactly one delimiter */ - bad |= (seen_one == 0); + mbedtls_platform_zeroize(lhash, sizeof(lhash)); - /* Calculate message length */ - msg_len = remaining - msg_index - 1; - bad |= (msg_len == 0); - - /* Check output buffer size */ - bad |= (output_max_len < msg_len); - - if (bad) { + /* Single decision point on the accumulated bit. */ + if (bad != MBEDTLS_CT_FALSE) { *olen = 0; return PSA_ERROR_INVALID_ARGUMENT; } - /* Copy message in constant time */ - *olen = msg_len; - if (*olen > 0) { - memcpy(output, p + msg_index + 1, msg_len); + /* Padding is valid; from here the plaintext length is no longer + * secret (it is returned to the caller via *olen). */ + size_t plaintext_size = ilen - (size_t) (p - input); + if (plaintext_size > output_max_len) { + *olen = 0; + return PSA_ERROR_INVALID_ARGUMENT; } + *olen = plaintext_size; + if (plaintext_size != 0) { + /* memmove (not memcpy): the driver's caller aliases input and + * output to the same buffer, so the source range [p, p+plaintext_size) + * overlaps the destination range [output, output+plaintext_size). + * Both pointers and the length are public, so memmove's access + * pattern stays fixed by public values -- CT property preserved. */ + memmove(output, p, plaintext_size); + } return PSA_SUCCESS; } #endif /* CONFIG_MBEDTLS_SSL_PROTO_TLS1_3 */