Decrypt using BcryptDecrypt

[Mandar Apte]

Any help regarding request in below email ?

On Wed, 10 Jun 2020, 10:08 pm Mandar Apte, <mandar.apte409 at gmail.com> wrote:

> Hello Team,
>
>           Are there any APIs in Libgcrypt using which I can get padded
> data along with my plain text data which I can encrypt using
> gcry_cipher_encrypt?
>
>
> Thanks in advance.
> Best Regards,
> Mandar
>
> On Fri, 5 Jun 2020, 7:16 pm Mandar Apte, <mandar.apte409 at gmail.com> wrote:
>
>> Hello Werner,
>>
>>           Thank you very much for the response.
>>
>> The way you have shown in the email chain below, I had done same thing in
>> my code as well. Also, I am passing the data of block length size only to
>> gcry_cipher_encrypt and gcry_cipher_decrypt APIs.
>> Now, my goal is to check, if the AES256 encryption/decryption is same for
>> libgcrypt and Bcrypt library. Thats the reason I am trying to decrypt the
>> data, which was encrypted using Libgcrypt APIs, using Bcrypt APIs on
>> windows.
>>
>> I am pretty sure if I use windows version of Libgcrypt my problem wont be
>> there at all.
>>
>> I think I myself have to handle the padding while encrypting using
>> Libgcrypt library APIs.
>>
>> Since, I have to handle padding in my code, is there any APIs in
>> libgcrypt with which I ensure that I am padding the data in standard way?
>>
>
>
> Are there any APIs in Libgcrypt using which I can get padded data along
>> with my plain text data which I can encrypt using gcry_cipher_encrypt?
>>
>>
>> Thank you in advance.
>> Best Regards,
>> Mandar
>>
>>
>>
>> On Fri, 5 Jun 2020, 2:05 pm Werner Koch, <wk at gnupg.org> wrote:
>>
>>> On Tue,  2 Jun 2020 16:57, Mandar Apte said:
>>> > On windows I am using Bcrypt library which also supports AES 256 in CBC
>>> > mode.
>>>
>>> FWIW, Libgcrypt runs very well on Windows.
>>>
>>> > Hence, I wanted to check, if the Libgcrypt APIs are doing padding
>>> > internally since I am not passing any such instruction to the Libgcrypt
>>> > library explicitly?
>>>
>>> No, Libgcrypt does not do any padding and it expects complete blocks.
>>> gcry_cipher_get_algo_blklen() tells you the block length of the cipher
>>> algorithm.
>>>
>>> There is a flag to enable ciphertext stealing (GCRY_CIPHER_CBC_CTS) but
>>> in this case you need to pass the entire plaintext/ciphertext to the
>>> encrypt/decrypt function; there is no way to do this incremental.
>>>
>>> For the standard padding as used in CMS (S/MIME), you need to handle the
>>> padding in your code; here is a snippet
>>>
>>>  if (last_block_is_incomplete)
>>>    {
>>>       int i,
>>>       int npad = blklen - (buflen % blklen);
>>>
>>>       p = buffer;
>>>       for (n=buflen, i=0; n < bufsize && i < npad; n++, i++)
>>>         p[n] = npad;
>>>       gcry_cipher_encrypt (chd, buffer, n, buffer, n);
>>>     }
>>>
>>>
>>>
>>> Shalom-Salam,
>>>
>>>    Werner
>>>
>>>
>>> --
>>> Die Gedanken sind frei.  Ausnahmen regelt ein Bundesgesetz.
>>>
>>
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