[saag] RSA-PSS

Russ Housley <housley@vigilsec.com> Wed, 04 December 2013 11:05 UTC

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From: Russ Housley <housley@vigilsec.com>
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Date: Wed, 4 Dec 2013 06:04:57 -0500
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Subject: [saag] RSA-PSS
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We have known for a very long time that PKCS #1 Version 1.5 (see RFC 2313) signature is more fragile than we might like.  PKCS #1 Version 1.5 signatures were developed in an ad hoc manner; RSASSA-PSS as specified in PKCS #1 Version 2.1 (see RFC 3447) was developed based on mathematical foundations.

I am aware of two attacks against PKCS #1 Version 1.5 implementations:

First, the Bleichenbacher attack against implementations.  In this attack, implementations do not calculate the length of the padding, but rather scan the 0xff at the beginning until they find a 0x00 byte.  Also, a small RSA exponent (for example e=3).

Second, fault-based attacks described by Boneh and others.  By injecting random faults into the RSA calculations, the attacker is able to regenerate the private key from the knowledge of faulty signatures.

RSA-PSS offers significant improvement against both of these attacks.

We have seen very little movement toward RSA-PSS.  While we are reviewing algorithm choices in light of the pervasive surveillance situation, I think we should take the time to consider improvements in our algorithm choices.

Russ