Hi,
I only used the CCM example that contains the same comment at the
comparable point in its code.
If I remember correctly this comment means that no data will be added
to outbuf. Hence, outlen should be 0. I have not stepped through the
code, but that seems to be meaningful as CCM and GCM use counter modes
and therefore do not require padding (reference:
http://openssl.6102.n7.nabble.com/AES-GCM-padding-td43598.html and
various GCM documentations). Hence, there is nothing to do for the
finalization except for computing the MAC (but I have not checked in the
code if the finalization really computes the MAC).
If this is correct, you _should_ check the return value, but as
mentioned above, outlen will be 0.
Note: Please take this as ideas/hints that I provide to you for further
testing as I am also not sure about this. Unfortunately, I do not have
time to check this on my own now.
Regards
Jens
On 06/06/2014 05:37 AM, Anant Rao wrote:
Thanks for the info!
I looked at the demos programs in the given link
http://git.openssl.org/gitweb/?p=openssl.git;a=blob;f=demos/evp/aesgcm.c;h=324d8a55b1481c507c7754fa7f33c30a02bdb737;hb=HEAD
.
I have a question in encrypt:
...
/* Finalise: note get no output for GCM */
63
http://git.openssl.org/gitweb/?p=openssl.git;a=blob;f=demos/evp/aesgcm.c;h=324d8a55b1481c507c7754fa7f33c30a02bdb737;hb=HEAD#l63
EVP_EncryptFinal_ex(ctx, outbuf, outlen);
...
What does this mean? That we shouldn't expect any output from this call
and/or that we should ignore it?
Thanks!
On Tue, May 27, 2014 at 12:33 AM, Jens Hiller
jens.hiller.c...@hotmail.de mailto:jens.hiller.c...@hotmail.de wrote:
On 05/27/2014 09:00 AM, Anant Rao wrote:
Hi,
I have ciphertext encrypted in Java (using BouncyCastle - BC) with
AES/GCM/NoPadding cipher.
When I tried to decrypt it using OpenSSL in a 'c' program, the
last call
'EVP_DecryptFinal_ex' fails. Somehow, ERR_print_errors_fp is not
printing anything either.
I do have the IV that is used in the Java's encrypt. However, I don't
know where BC stores the tag in the ciphertext. I tried it at the
beginning and the end of the ciphertext, but it didn't help.
That is, I tried both of the following in the decrypt:
|IV|TAG|Ciphertext
|IV|Ciphertext|TAG
Both didn't work.
I tried both of the following as well with the same failure:
EVP_aes_256_gcm
EVP_aes_128_gcm
I have run out of ideas what else to try. Any help would be greatly
appreciated.
Thanks in advance!
Have a look at
https://www.openssl.org/docs/crypto/EVP_EncryptInit.html#GCM_Mode
and at the example in 'openssl/demos/evp/aesgcm.c' of the current master
branch (git://git.openssl.org/openssl.git
http://git.openssl.org/openssl.git).
Regards
Jens
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