Date: Mon, 13 Mar 2017 22:06:39 +0000 From: Steven Chamberlain <steven@pyro.eu.org> To: freebsd-security@freebsd.org, freebsd-hackers@freebsd.org Subject: Re: arc4random weakness (was: WikiLeaks CIA Exploits: FreeBSD References Within) Message-ID: <20170313220639.GB65190@pyro.eu.org> In-Reply-To: <CAD2Ti28acbW%2BpGQR5UihECWvg9WduGmVzkVFug_2ZWRF2zyTBw@mail.gmail.com> References: <CAD2Ti28acbW%2BpGQR5UihECWvg9WduGmVzkVFug_2ZWRF2zyTBw@mail.gmail.com>
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--E13BgyNx05feLLmH Content-Type: multipart/mixed; boundary="MW5yreqqjyrRcusr" Content-Disposition: inline --MW5yreqqjyrRcusr Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable =46rom this document (TOP SECRET//SI//NOFORN): https://wikileaks.org/ciav7p1/cms/files/NOD%20Cryptographic%20Requirements%= 20v1.1%20TOP%20SECRET.pdf version 1.0 said: | 8. (S//NF) [...] If RC4 is used, at least the first 1024 | bytes of the cryptostream must be discarded and may not be used and that is exactly what FreeBSD's libc and in-kernel arc4random implementations do. version 1.1 received input from another agency: | (C//SI//REL FVEY) Coordinated with NSA/CES. and a new requirement was introduced: | (TS//SI) 5.9: Added additional information about proper use of RC4. | 9. (TS//SI) Further than stated above, if RC4 is used the first 3072 | bytes of the cryptostream must be discarded and may not be used. I think you should take that to mean, the NSA has, or suspects someone else to have, a practical attack on RC4 when being used as FreeBSD does currently. The document seems 4-5 years old already as it prohibits use of RC4 at all from 2014 onward. Please consider switching to ChaCha20 in the long term (kern/182610), but right now, at least increase the amount of early keystream that is discarded. Many thanks, Regards, --=20 Steven Chamberlain steven@pyro.eu.org --MW5yreqqjyrRcusr Content-Type: text/x-diff; charset=us-ascii Content-Disposition: attachment; filename="arc4random.patch" Content-Transfer-Encoding: quoted-printable diff -Nru a/head/lib/libc/gen/arc4random.c b/head/lib/libc/gen/arc4random.c --- a/head/lib/libc/gen/arc4random.c 2016-10-12 14:56:14.834409000 +0100 +++ b/head/lib/libc/gen/arc4random.c 2017-03-13 21:57:16.532833171 +0000 @@ -160,7 +160,7 @@ * Discard early keystream, as per recommendations in: * "(Not So) Random Shuffles of RC4" by Ilya Mironov. */ - for (i =3D 0; i < 1024; i++) + for (i =3D 0; i < 3072; i++) (void)arc4_getbyte(); arc4_count =3D 1600000; } diff -Nru a/head/sys/libkern/arc4random.c b/head/sys/libkern/arc4random.c --- a/head/sys/libkern/arc4random.c 2016-11-25 17:20:23.862538000 +0000 +++ b/head/sys/libkern/arc4random.c 2017-03-13 21:58:45.985402563 +0000 @@ -84,11 +84,11 @@ /* * Throw away the first N words of output, as suggested in the * paper "Weaknesses in the Key Scheduling Algorithm of RC4" - * by Fluher, Mantin, and Shamir. (N =3D 256 in our case.) + * by Fluher, Mantin, and Shamir. (N =3D 768 in our case.) * * http://dl.acm.org/citation.cfm?id=3D646557.694759 */ - for (n =3D 0; n < 256*4; n++) + for (n =3D 0; n < 768*4; n++) arc4_randbyte(arc4); =20 mtx_unlock(&arc4->mtx); --MW5yreqqjyrRcusr-- --E13BgyNx05feLLmH Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQGcBAEBCAAGBQJYxxftAAoJEIzTM2ydu2CcKWcMAIXfG+Y5afRIKbmT2f6htJVO Kj4YK+CqFYc81W05yGFb1xr9RilgDXzNrMNwrbkHn9NJERI5IO0FLtdVI+x1Iund Bokjj2ZkkdkPg72y4V3fAnrKNMFMAzScCWtYccwioWFNPL2NvOpnqQDIuEqQ5qNb xcvtkWcV9Vrh5dIdNn+9Bf21g/Dh4YJ5tKkY965Oi3Sg/1Ij4zM73Jy07j8TRIrL 8siWn195tWnvFMQo151v9VY74l9WcoNd1rgC9bceMGl2/UNAIcnm0j/W5TWTw6mq t8GvTxVQFSvYB2dL7fNNOhP6hSVSb74xC6Tic1tjZM+Okd5EzbW3/FbrcdNWoof1 ZBibe5/HF7I117ITwJ1N0qq5VWdLaAaNKkC7tUOm66lOSQvStZXQDAimnIzPJuke 65dbFDpi1Arr9eFf88uPazh26K2jIdcUGt9Cgeaat6uXFxRW0xAzX81Lo1Ci0Ymk e4S0fExy4fj+tzYcOcsy4zmqy1kzFMBRXM/wm1ToBA== =/kTf -----END PGP SIGNATURE----- --E13BgyNx05feLLmH--
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