On Tue, Mar 05, 2013, Matt Caswell wrote: > On 5 March 2013 14:13, Dr. Stephen Henson <st...@openssl.org> wrote: > > > On Tue, Mar 05, 2013, Leon Brits wrote: > > > > > Just want to add that I do set the data sizes before EncryptUpdate and > > > DecryptUpdate and mentioned in the CCM section of the OpenSSL support > > page. > > > This page does answer both my questions (appologies), but I still fail to > > > decrypt. > > > > > > > I'll add an example for CCM mode in the demos section shortly. CCM mode is > > a > > bit picky about setting all the parameters correctly in the correct order. > > > > That would be good!! I am working on some test code myself but cannot get > it to work. See source code below. This is adapted from some code I have > for GCM that works fine. With CCM though encryption (apparently) works > fine, but when I get to decryption I get a 0 response from the final > EVP_DecryptUpdate call - no error message on the OpenSSL error stack :-( >
I'd just committed it, it's very similar to the GCM code but with some additional restrictions. The main one is that you can only call EVP_*Update once for AAD and/or the ciphertext/plaintext: this is mainly influenced by the requirement that you cannot reveal any plaintext if the tag verify fails. As a result the tag verify is performed when you call EVP_DecryptUpdate and is reflected by the return value: there is no call to EVP_DecryptFinal. See demos/evp/aesccm.c in the master branch. I'll update the manual page too. Steve. -- Dr Stephen N. Henson. OpenSSL project core developer. Commercial tech support now available see: http://www.openssl.org ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List openssl-dev@openssl.org Automated List Manager majord...@openssl.org
