* ext/openssl/ossl_cipher.c: Add warning about key as IV.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34463 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 6 insertions, 0 deletions

diff --git a/ext/openssl/ossl_cipher.c b/ext/openssl/ossl_cipher.c
index 101ea052fa..4e758b6a26 100644
--- a/ext/openssl/ossl_cipher.c
+++ b/ext/openssl/ossl_cipher.c
@@ -686,6 +686,12 @@ Init_ossl_cipher(void)
      *  key = cipher.random_key
      *  iv = cipher.random_iv # also sets the generated IV on the Cipher
      *
+     *  Although the key is generally a random value, too, it is a bad choice
+     *  as an IV. There are elaborate ways how an attacker can take advantage
+     *  of such an IV. As a general rule of thumb, exposing the key directly
+     *  or indirectly should be avoided at all cost and exceptions only be
+     *  made with good reason. 
+     *
      * === Calling Cipher#final
      *
      * ECB (which should not be used) and CBC are both block-based modes.