Attachment 1597 Details for Bug 1550 – Patch from Damien Miller to enable AES-256 in ssh-keygen

[patch] Patch from Damien Miller to enable AES-256 in ssh-keygen

tmp.msg (text/plain), 2.27 KB, created by Jim Knoble on 2009-01-23 07:03:40 AEDT

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Creator: Jim Knoble

Created: 2009-01-23 07:03:40 AEDT

Size: 2.27 KB

patch

obsolete

>Date: Tue, 20 Jan 2009 18:30:23 +1100 (EST)
>From: Damien Miller <djm@mindrot.org>
>To: Jim Knoble <jmknoble@pobox.com>
>cc: OpenSSH Devel <openssh-unix-dev@mindrot.org>
>Subject: Re: OpenSSH private key encryption: time for AES?
>In-Reply-To: <20090120060635.GA29074@crawfish.ais.com>
>Message-ID: <alpine.BSO.1.10.0901201822540.5492@fuyu.mindrot.org>
>References: <20090120060635.GA29074@crawfish.ais.com>
>
>On Tue, 20 Jan 2009, Jim Knoble wrote:
>
>> Hi, all.
>> 
>> So, in reviewing my OpenSSH keypairs and evaluating the size my RSA keys
>> should be, i realized that, if i update my 2048-bit keypairs to 4096
>> bits, it really doesn't matter that much, because they're still
>> only encrypted with 3DES, which provides an effective 112 bits of
>> symmetric encryption strength:
>> 
>>     $ head -4 ~/.ssh/id_rsa
>>     -----BEGIN RSA PRIVATE KEY-----
>>     Proc-Type: 4,ENCRYPTED
>>     DEK-Info: DES-EDE3-CBC,XXXXXXXXXXXXXXXX
>> 
>>     $ 
>> 
>> According to NIST[1][2], a minimum of 112-bit symmetric / 2048-bit
>> asymmetric keystrength is recommended for protection up until about
>> 2030.  For protection beyond 2030, or for the paranoid, larger keysizes
>> are recommended.  Other recommendations (e.g., those of ECRYPT) vary in
>> how long 112/2048-bit encryption should last.
>> 
>> With that in mind ... how can i encrypt my 4096-bit SSH RSA keypair with
>> something like AES-128, AES-256, or Twofish instead of 3DES and still
>> use it with OpenSSH?  Can ssh-add read (unencrypted) key data from stdin?
>
>If you want to change it then you can do something like this. It
>probably wouldn't hurt to change - new installations will still be able
>to read old keys
>
>Index: authfile.c
>===================================================================
>RCS file: /cvs/src/usr.bin/ssh/authfile.c,v
>retrieving revision 1.76
>diff -u -p -r1.76 authfile.c
>--- authfile.c	3 Aug 2006 03:34:41 -0000	1.76
>+++ authfile.c	20 Jan 2009 07:22:48 -0000
>@@ -182,7 +182,7 @@ key_save_private_pem(Key *key, const cha
> 	int success = 0;
> 	int len = strlen(_passphrase);
> 	u_char *passphrase = (len > 0) ? (u_char *)_passphrase : NULL;
>-	const EVP_CIPHER *cipher = (len > 0) ? EVP_des_ede3_cbc() : NULL;
>+	const EVP_CIPHER *cipher = (len > 0) ? EVP_aes_256_cbc() : NULL;
> 
> 	if (len > 0 && len <= 4) {
> 		error("passphrase too short: have %d bytes, need > 4", len);
>
>

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