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Improve & test legacy mbedtls_pkcs5_pbe2

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* Prevent pkcs5_pbe2 encryption when PKCS7 padding has been
  disabled since this not part of the specs.
* Allow decryption when PKCS7 padding is disabled for legacy
  reasons, However, invalid padding is not checked.
* Add tests to check these scenarios. Test data has been
  reused but with changing padding data in last block to
  check for valid/invalid padding.
* Document new behaviour, known limitations and possible
  security concerns.

Signed-off-by: Waleed Elmelegy <waleed.elmelegy@arm.com>
This commit is contained in:
Waleed Elmelegy
2023-07-19 14:01:35 +01:00
parent caa6a1fd0d
commit 708d78f80b
4 changed files with 100 additions and 5 deletions
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18
library/pkcs5.c
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@ -203,6 +203,24 @@ int mbedtls_pkcs5_pbes2(const mbedtls_asn1_buf *pbe_params, int mode,
goto exit;
}
/* PKCS5 uses CBC with PKCS7 padding (which is the same as
* "PKCS5 padding" except that it's typically only called PKCS5
* with 64-bit-block ciphers).
*/
mbedtls_cipher_padding_t padding = MBEDTLS_PADDING_PKCS7;
#if !defined(MBEDTLS_CIPHER_PADDING_PKCS7)
/* For historical reasons, when decrypting, this function works when
* decrypting even when support for PKCS7 padding is disabled. In this
* case, it ignores the padding, and so will never report a
* password mismatch.
*/
if (mode == MBEDTLS_DECRYPT)
padding = MBEDTLS_PADDING_NONE;
#endif
if ((ret = mbedtls_cipher_set_padding_mode(&cipher_ctx, padding)) != 0) {
goto exit;
}
if ((ret = mbedtls_cipher_crypt(&cipher_ctx, iv, enc_scheme_params.len,
data, datalen, output, &olen)) != 0) {
ret = MBEDTLS_ERR_PKCS5_PASSWORD_MISMATCH;