Move testing of mbedtls_ssl_decrypt_buf to a new test suite
test_suite_ssl is huge and needs splitting.
Create a new test suite focused on mbedtls_ssl_decrypt_buf(), which is a
complicated function that needs more thorough testing with malformed inputs.
At this point, we are only doing negative testing with CBC-non-ETM test
suites. This needs to grow.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ssl_decrypt.function b/tests/suites/test_suite_ssl_decrypt.function
new file mode 100644
index 0000000..84abe2f
--- /dev/null
+++ b/tests/suites/test_suite_ssl_decrypt.function
@@ -0,0 +1,243 @@
+/* BEGIN_HEADER */
+/* Testing of mbedtls_ssl_decrypt_buf() specifically, focusing on negative
+ * testing (using malformed inputs). */
+
+#include <mbedtls/ssl.h>
+#include <ssl_misc.h>
+#include <test/ssl_helpers.h>
+
+/* END_HEADER */
+
+/* BEGIN_DEPENDENCIES
+ * depends_on:MBEDTLS_SSL_TLS_C
+ * END_DEPENDENCIES
+ */
+
+/* BEGIN_CASE depends_on:MBEDTLS_CIPHER_MODE_CBC:MBEDTLS_AES_C:MBEDTLS_SSL_PROTO_TLS1_2 */
+void ssl_decrypt_non_etm_cbc(int cipher_type, int hash_id, int trunc_hmac,
+ int length_selector)
+{
+ /*
+ * Test record decryption for CBC without EtM, focused on the verification
+ * of padding and MAC.
+ *
+ * Actually depends on TLS 1.2 and either AES, ARIA or Camellia, but since
+ * the test framework doesn't support alternation in dependency statements,
+ * just depend on AES.
+ *
+ * The length_selector argument is interpreted as follows:
+ * - if it's -1, the plaintext length is 0 and minimal padding is applied
+ * - if it's -2, the plaintext length is 0 and maximal padding is applied
+ * - otherwise it must be in [0, 255] and is padding_length from RFC 5246:
+ * it's the length of the rest of the padding, that is, excluding the
+ * byte that encodes the length. The minimal non-zero plaintext length
+ * that gives this padding_length is automatically selected.
+ */
+ mbedtls_ssl_context ssl; /* ONLY for debugging */
+ mbedtls_ssl_transform t0, t1;
+ mbedtls_record rec, rec_save;
+ unsigned char *buf = NULL, *buf_save = NULL;
+ size_t buflen, olen = 0;
+ size_t plaintext_len, block_size, i;
+ unsigned char padlen; /* excluding the padding_length byte */
+ unsigned char add_data[13];
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+ psa_mac_operation_t operation = PSA_MAC_OPERATION_INIT;
+ size_t sign_mac_length = 0;
+ unsigned char mac[PSA_HASH_MAX_SIZE];
+#else
+ unsigned char mac[MBEDTLS_MD_MAX_SIZE];
+#endif
+ int exp_ret;
+ int ret;
+ const unsigned char pad_max_len = 255; /* Per the standard */
+
+ mbedtls_ssl_init(&ssl);
+ mbedtls_ssl_transform_init(&t0);
+ mbedtls_ssl_transform_init(&t1);
+ MD_OR_USE_PSA_INIT();
+
+ /* Set up transforms with dummy keys */
+ ret = mbedtls_test_ssl_build_transforms(&t0, &t1, cipher_type, hash_id,
+ 0, trunc_hmac,
+ MBEDTLS_SSL_VERSION_TLS1_2,
+ 0, 0);
+
+ TEST_ASSERT(ret == 0);
+
+ /* Determine padding/plaintext length */
+ TEST_ASSERT(length_selector >= -2 && length_selector <= 255);
+ block_size = t0.ivlen;
+ if (length_selector < 0) {
+ plaintext_len = 0;
+
+ /* Minimal padding
+ * The +1 is for the padding_length byte, not counted in padlen. */
+ padlen = block_size - (t0.maclen + 1) % block_size;
+
+ /* Maximal padding? */
+ if (length_selector == -2) {
+ padlen += block_size * ((pad_max_len - padlen) / block_size);
+ }
+ } else {
+ padlen = length_selector;
+
+ /* Minimal non-zero plaintext_length giving desired padding.
+ * The +1 is for the padding_length byte, not counted in padlen. */
+ plaintext_len = block_size - (padlen + t0.maclen + 1) % block_size;
+ }
+
+ /* Prepare a buffer for record data */
+ buflen = block_size
+ + plaintext_len
+ + t0.maclen
+ + padlen + 1;
+ TEST_CALLOC(buf, buflen);
+ TEST_CALLOC(buf_save, buflen);
+
+ /* Prepare a dummy record header */
+ memset(rec.ctr, 0, sizeof(rec.ctr));
+ rec.type = MBEDTLS_SSL_MSG_APPLICATION_DATA;
+ mbedtls_ssl_write_version(rec.ver, MBEDTLS_SSL_TRANSPORT_STREAM,
+ MBEDTLS_SSL_VERSION_TLS1_2);
+#if defined(MBEDTLS_SSL_DTLS_CONNECTION_ID)
+ rec.cid_len = 0;
+#endif /* MBEDTLS_SSL_DTLS_CONNECTION_ID */
+
+ /* Prepare dummy record content */
+ rec.buf = buf;
+ rec.buf_len = buflen;
+ rec.data_offset = block_size;
+ rec.data_len = plaintext_len;
+ memset(rec.buf + rec.data_offset, 42, rec.data_len);
+
+ /* Serialized version of record header for MAC purposes */
+ memcpy(add_data, rec.ctr, 8);
+ add_data[8] = rec.type;
+ add_data[9] = rec.ver[0];
+ add_data[10] = rec.ver[1];
+ add_data[11] = (rec.data_len >> 8) & 0xff;
+ add_data[12] = (rec.data_len >> 0) & 0xff;
+
+ /* Set dummy IV */
+ memset(t0.iv_enc, 0x55, t0.ivlen);
+ memcpy(rec.buf, t0.iv_enc, t0.ivlen);
+
+ /*
+ * Prepare a pre-encryption record (with MAC and padding), and save it.
+ */
+
+ /* MAC with additional data */
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+ TEST_EQUAL(PSA_SUCCESS, psa_mac_sign_setup(&operation,
+ t0.psa_mac_enc,
+ t0.psa_mac_alg));
+ TEST_EQUAL(PSA_SUCCESS, psa_mac_update(&operation, add_data, 13));
+ TEST_EQUAL(PSA_SUCCESS, psa_mac_update(&operation,
+ rec.buf + rec.data_offset,
+ rec.data_len));
+ TEST_EQUAL(PSA_SUCCESS, psa_mac_sign_finish(&operation,
+ mac, sizeof(mac),
+ &sign_mac_length));
+#else
+ TEST_EQUAL(0, mbedtls_md_hmac_update(&t0.md_ctx_enc, add_data, 13));
+ TEST_EQUAL(0, mbedtls_md_hmac_update(&t0.md_ctx_enc,
+ rec.buf + rec.data_offset,
+ rec.data_len));
+ TEST_EQUAL(0, mbedtls_md_hmac_finish(&t0.md_ctx_enc, mac));
+#endif
+
+ memcpy(rec.buf + rec.data_offset + rec.data_len, mac, t0.maclen);
+ rec.data_len += t0.maclen;
+
+ /* Pad */
+ memset(rec.buf + rec.data_offset + rec.data_len, padlen, padlen + 1);
+ rec.data_len += padlen + 1;
+
+ /* Save correct pre-encryption record */
+ rec_save = rec;
+ rec_save.buf = buf_save;
+ memcpy(buf_save, buf, buflen);
+
+ /*
+ * Encrypt and decrypt the correct record, expecting success
+ */
+ TEST_EQUAL(0, mbedtls_test_psa_cipher_encrypt_helper(
+ &t0, t0.iv_enc, t0.ivlen, rec.buf + rec.data_offset,
+ rec.data_len, rec.buf + rec.data_offset, &olen));
+ rec.data_offset -= t0.ivlen;
+ rec.data_len += t0.ivlen;
+
+ TEST_EQUAL(0, mbedtls_ssl_decrypt_buf(&ssl, &t1, &rec));
+
+ /*
+ * Modify each byte of the pre-encryption record before encrypting and
+ * decrypting it, expecting failure every time.
+ */
+ for (i = block_size; i < buflen; i++) {
+ mbedtls_test_set_step(i);
+
+ /* Restore correct pre-encryption record */
+ rec = rec_save;
+ rec.buf = buf;
+ memcpy(buf, buf_save, buflen);
+
+ /* Corrupt one byte of the data (could be plaintext, MAC or padding) */
+ rec.buf[i] ^= 0x01;
+
+ /* Encrypt */
+ TEST_EQUAL(0, mbedtls_test_psa_cipher_encrypt_helper(
+ &t0, t0.iv_enc, t0.ivlen, rec.buf + rec.data_offset,
+ rec.data_len, rec.buf + rec.data_offset, &olen));
+ rec.data_offset -= t0.ivlen;
+ rec.data_len += t0.ivlen;
+
+ /* Decrypt and expect failure */
+ TEST_EQUAL(MBEDTLS_ERR_SSL_INVALID_MAC,
+ mbedtls_ssl_decrypt_buf(&ssl, &t1, &rec));
+ }
+
+ /*
+ * Use larger values of the padding bytes - with small buffers, this tests
+ * the case where the announced padlen would be larger than the buffer
+ * (and before that, than the buffer minus the size of the MAC), to make
+ * sure our padding checking code does not perform any out-of-bounds reads
+ * in this case. (With larger buffers, ie when the plaintext is long or
+ * maximal length padding is used, this is less relevant but still doesn't
+ * hurt to test.)
+ *
+ * (Start the loop with correct padding, just to double-check that record
+ * saving did work, and that we're overwriting the correct bytes.)
+ */
+ for (i = padlen; i <= pad_max_len; i++) {
+ mbedtls_test_set_step(i);
+
+ /* Restore correct pre-encryption record */
+ rec = rec_save;
+ rec.buf = buf;
+ memcpy(buf, buf_save, buflen);
+
+ /* Set padding bytes to new value */
+ memset(buf + buflen - padlen - 1, i, padlen + 1);
+
+ /* Encrypt */
+ TEST_EQUAL(0, mbedtls_test_psa_cipher_encrypt_helper(
+ &t0, t0.iv_enc, t0.ivlen, rec.buf + rec.data_offset,
+ rec.data_len, rec.buf + rec.data_offset, &olen));
+ rec.data_offset -= t0.ivlen;
+ rec.data_len += t0.ivlen;
+
+ /* Decrypt and expect failure except the first time */
+ exp_ret = (i == padlen) ? 0 : MBEDTLS_ERR_SSL_INVALID_MAC;
+ TEST_EQUAL(exp_ret, mbedtls_ssl_decrypt_buf(&ssl, &t1, &rec));
+ }
+
+exit:
+ mbedtls_ssl_free(&ssl);
+ mbedtls_ssl_transform_free(&t0);
+ mbedtls_ssl_transform_free(&t1);
+ mbedtls_free(buf);
+ mbedtls_free(buf_save);
+ MD_OR_USE_PSA_DONE();
+}
+/* END_CASE */