add encrypt-then-mac (EtM) modes to openssh by defining new mac algorithms

that change the packet format and compute the MAC over the encrypted
message (including the packet size) instead of the plaintext data;
these EtM modes are considered more secure and used by default.
feedback and ok djm@

1 files changed, 17 insertions, 5 deletions

diff --git a/usr.bin/ssh/cipher.c b/usr.bin/ssh/cipher.c
index 3acc4182976..c7fb2628947 100644
--- a/usr.bin/ssh/cipher.c
+++ b/usr.bin/ssh/cipher.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: cipher.c,v 1.82 2009/01/26 09:58:15 markus Exp $ */
+/* $OpenBSD: cipher.c,v 1.83 2012/12/11 22:31:18 markus Exp $ */
 /*
  * Author: Tatu Ylonen <ylo@cs.hut.fi>
  * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
@@ -253,13 +253,25 @@ cipher_init(CipherContext *cc, Cipher *cipher,
 	}
 }
 
+/*
+ * cipher_crypt() operates as following:
+ * Copy 'aadlen' bytes (without en/decryption) from 'src' to 'dest'.
+ * Theses bytes are treated as additional authenticated data for
+ * authenticated encryption modes.
+ * En/Decrypt 'len' bytes at offset 'aadlen' from 'src' to 'dest'.
+ * Both 'aadlen' and 'authlen' can be set to 0.
+ */
 void
-cipher_crypt(CipherContext *cc, u_char *dest, const u_char *src, u_int len)
+cipher_crypt(CipherContext *cc, u_char *dest, const u_char *src,
+    u_int len, u_int aadlen)
 {
+	if (aadlen)
+		memcpy(dest, src, aadlen);
 	if (len % cc->cipher->block_size)
-		fatal("cipher_encrypt: bad plaintext length %d", len);
-	if (EVP_Cipher(&cc->evp, dest, (u_char *)src, len) == 0)
-		fatal("evp_crypt: EVP_Cipher failed");
+		fatal("%s: bad plaintext length %d", __func__, len);
+	if (EVP_Cipher(&cc->evp, dest + aadlen, (u_char *)src + aadlen,
+	    len) < 0)
+		fatal("%s: EVP_Cipher failed", __func__);
 }
 
 void