Bug #8667

Unable to set OpenSSL GCM iv_length in Ruby

Added by Anonymous over 1 year ago. Updated 3 days ago.

ruby -v:- Backport:1.9.3: UNKNOWN, 2.0.0: UNKNOWN



In OpenSSL you are allowed to change the iv_length on an AES-BCM cipher. (
http://www.openssl.org/docs/crypto/EVP_EncryptInit.html#GCM_Mode) However
this was not implemented in the ruby-wrapper. Since I am a novice in C and
OpenSSL I think by no means my supplied patch is complete, it is a start
however. Maybe this missing function can be added to Ruby 2.0?

You can now set the iv_length using:

cipher = OpenSSL::Cipher.new('aes-128-gcm').encrypt
cipher.iv_len = 16

An issue I already spotted is that OpenSSL sets the ivlen on the
cipher_data (snippet from OpenSSL crypto/evp/e_aes.c):
EVP_AES_GCM_CTX *gctx = c->cipher_data;
gctx->ivlen = arg;

and not the c->cipher->iv_len. So querying for the iv_len in ruby by using
cipher.iv_len will still report the default which is 12. Encryption however
is done correctly using the new iv-length. I tested it by comparing it to
results from other programming languages (Java and C#).

Regards Andres

ossl_set_iv_length.patch Magnifier (1.25 KB) Anonymous, 07/23/2013 08:02 AM

0001-Alternate-implementation-of-gcm-IV-length-support.patch Magnifier - against trunk (2.01 KB) David Waite, 05/04/2014 06:31 PM


#1 Updated by Eric Hodel over 1 year ago

  • Category set to ext/openssl
  • Status changed from Open to Assigned
  • Assignee set to Martin Bosslet
  • ruby -v set to -

#2 Updated by David Waite 11 months ago

Alternate patch which makes iv length changes implicit in iv= when using GCM.

This issue currently requires me to require a patched ruby for my software to run.

#3 Updated by Zachary Scott 3 days ago

  • Assignee changed from Martin Bosslet to openssl

Without knowing what HAVE_AUTHENTICATED_ENCRYPTION is, I'm not really sure.. also we need a test for this.

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