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Cisco Bug: CSCvh84754 - DKIM fails signing and verification messages with an empty body on 'relaxed' canonicalization

Last Modified

Mar 26, 2019

Products (1)

  • Cisco Email Security Appliance

Known Affected Releases

11.0.1-027 11.0.1-028

Description (partial)

Symptom:
The implemented method for 'relaxed' body canonicalization algorithm wrongly process an empty body. 
An empty body returned for the 'relaxed' mode gives the same hash as the empty body for a 'simple' mode.
Because of the issue in canonicalization method and 'relaxed' mode for an empty body the body hash is wrongly calculated. This can results with "body hash did not verify [final]" error for RFC compliant verifier.

As the same method is used to canonicalized a message for signing and verification this cause two issue.
- properly signed message by a third-party signer  will fail body hashverification on ESA 
- wrongly signed message on ESA will not be properly verify by a third-party verifier

Conditions:
An empty body message canonicalized in 'relaxed' mode.  The body hash calculated for an empty body and 'relaxed' mode gives the same value as in 'simple' mode. The value is 'frcCV1k9oG9oKj3dpUqdJg1PxRT2RSN/XKdLCPjaYaY='
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