Date: Tue, 14 Jul 2009 22:00:18 +0200 From: Florian Weimer <fw@...eb.enyo.de> To: oss-security@...ts.openwall.com Subject: Fixing the XML signature HMAC truncation authentication bypass Quoting from <http://www.kb.cert.org/vuls/id/466161>: | XML Signature Syntax and Processing (XMLDsig) is a W3C | recommendation for providing integrity, message authentication, | and/or signer authentication services for data. XMLDsig is commonly | used by web services such as SOAP. The XMLDsig recommendation | includes support for HMAC truncation, as specified in RFC2014. When | HMAC truncation is under the control of an attacker, however, this | can result in an effective authentication bypass. For example, by | specifying an HMACOutputLength of 1, only one bit of the signature | is verified. This can allow an attacker to forge an XML signature | that will be accepted as valid. What shall we do about this? Shall we just cap the value at 80 or 96 bits in our implementations?
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