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 > ______________________________________________________________________ > OpenSSL Project http://www.openssl.org > User Support Mailing List > openssl-users@openssl.org <mailto:openssl-users@openssl.org> > Automated List Manager > majord...@openssl.org <mailto:majord...@openssl.org> > > > > > -- > > *Anant** **Rao* > Server Lead > D / a...@noknok.com <mailto:a...@noknok.com> > > *Nok Nok Labs Inc.* > 4151 Middlefield Road, Suite 200 > Palo Alto, CA 94303 > T +1 650 433 1300 > i...@noknok.com <mailto:i...@noknok.com> > > *www.noknok.com* <http://www.noknok.com> > > > > > > > > <http://www.linkedin.com/company/nok-nok-labs> > <http://www.twitter.com/noknoklabs> > <https://plus.google.com/108217184383559859585> > <http://www.facebook.com/NokNokLabs> > > ______________________________________________________________________ OpenSSL Project http://www.openssl.org User Support Mailing List openssl-users@openssl.org Automated List Manager majord...@openssl.org
