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Bug 23097 - Underspecified behavior of verify() with regards to truncated signature
Summary: Underspecified behavior of verify() with regards to truncated signature
Status: RESOLVED WORKSFORME
Alias: None
Product: Web Cryptography
Classification: Unclassified
Component: Web Cryptography API Document (show other bugs)
Version: unspecified
Hardware: PC Linux
: P2 normal
Target Milestone: ---
Assignee: Ryan Sleevi
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Reported: 2013-08-30 01:19 UTC by Eric Roman
Modified: 2014-02-28 16:17 UTC (History)
2 users (show)

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Description Eric Roman 2013-08-30 01:19:13 UTC 
If verify() is called with a signature that is smaller than expected:
  - Does it do a truncated comparison?
  - Or does it fail verification

My expectation is that it should fail verification.
Comment 1 Mark Watson 2014-02-28 16:17:57 UTC 
With the exception of HMAC, the signature comparison is done in the procedures of referenced specification for each cryptographic operation. So this is out of our scope, but I would be very surprised if any of those specifications did a tuncated comparison.

For HMAC we ask if the provided MAC is 'equal' to the calculated one. Two octet strings of different lengths are not 'equal', so verification would certainly fail if the provided MAC was the wrong length.