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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 27d8c21a87
commit 412629c815
4 changed files with 100 additions and 5 deletions
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25
include/mbedtls/pkcs5.h
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@@ -57,13 +57,36 @@ extern "C" {
/**
* \brief PKCS#5 PBES2 function
*
* \note When encrypting, #MBEDTLS_CIPHER_PADDING_PKCS7 must
* be enabled at compile time.
*
* \warning When decrypting:
* - if #MBEDTLS_CIPHER_PADDING_PKCS7 is enabled at compile
* time, this function validates the CBC padding and returns
* #MBEDTLS_ERR_PKCS5_PASSWORD_MISMATCH if the padding is
* invalid. Note that this can help active adversaries
* attempting to brute-forcing the password. Note also that
* there is no guarantee that an invalid password will be
* detected (the chances of a valid padding with a random
* password are about 1/255).
* - if #MBEDTLS_CIPHER_PADDING_PKCS7 is disabled at compile
* time, this function does not validate the CBC padding.
*
* \param pbe_params the ASN.1 algorithm parameters
* \param mode either MBEDTLS_PKCS5_DECRYPT or MBEDTLS_PKCS5_ENCRYPT
* \param pwd password to use when generating key
* \param pwdlen length of password
* \param data data to process
* \param datalen length of data
* \param output output buffer
* \param output Output buffer.
* On success, it contains the decrypted data, possibly
* followed by the CBC padding.
* On failure, the content is indetermidate.
* For decryption, there must be enough room for \p datalen
* bytes.
* For encryption, there must be enough room for
* \p datalen + 1 bytes, rounded up to the block size of
* the block cipher identified by \p pbe_params.
*
* \returns 0 on success, or a MBEDTLS_ERR_XXX code if verification fails.
*/