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Date: Tue, 15 Nov 2011 08:20:29 +0400
From: Solar Designer <>
Cc: Colin Percival <>,
Subject: Re: OpenBSD bcrypt error return

On Tue, Nov 15, 2011 at 07:14:17AM +0400, Solar Designer wrote:
> The bcrypt implementation from OpenBSD, now also found in FreeBSD and
> NetBSD, returns a constant string on error.

Oh, and of course it is also in DragonFly:

> static char    error[] = ":";
> Clearly, ":" can't match a field value in an /etc/passwd-like file,
> which is great, but what happens if one of those errors occurs when
> setting a new password?  Luckily, the specific errors being checked for
> have to do with unsupported or invalid salt strings, so they can't
> happen on a properly configured system.  Nevertheless, this may be a
> disaster waiting to happen - e.g., if a new "$2" prefix is introduced
> (like I did when dealing with the crypt_blowfish bug), support for it is
> added to a password-changing program, but an appropriate update to libc
> or libcrypt is not yet deployed on a system.
> Thus, to avoid this disaster, this poor way of handling errors may also
> get in the way of adding support for such extra "$2" prefixes on *BSD,
> unfortunately.  This is something I forgot about when deciding on those
> this summer, even though I was aware of this issue in OpenBSD since 1998
> or so.
> Yes, I did report this issue to OpenBSD folks at least twice - last time
> this summer, after it was independently discovered by Zefram.
> Maybe FreeBSD and/or NetBSD will want to patch it, or at least to be
> aware of the risk - hence the posting in here.
> The fix may be to reuse the approach from crypt_blowfish:
> int _crypt_output_magic(const char *setting, char *output, int size)
> {
> 	if (size < 3)
> 		return -1;
> 	output[0] = '*';
> 	output[1] = '0';
> 	output[2] = '\0';
> 	if (setting[0] == '*' && setting[1] == '0')
> 		output[1] = '1';
> 	return 0;
> }
> This may be done in bcrypt.c or in wrapper code common for all crypt(3)
> hash types.
> Proactive security, anyone?
> Alexander

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