Tracking hash algorithm MTA option

Tracking hash function usage:  (hash algorithm name)
The  MTA option controls what hash algorithm the MTA uses to generate hashes of tracking and recall secrets for use with the MTQP protocol. The value should be a hash algorithm supported by the MTA, one of MD2, MD4, MD5, SHA1, SHA256, SHA512, MD128, or MD160. The default if this option is not specified is SHA1, as required by the MTQP protocol standard.

Important note: As of this writing (February 2020) there is no practical preimage attack on SHA-1, which is what would be required to attack its usage in MQTP. (All known practical attacks are collision attacks, which generate a collision for a known preimage.) As such, the only justification for switching to SHA-2 hash function is to meet compliance requirements, and the benefits of meeting such requirements in the absence of any technical justification must be carefully weighed against the costs of standards incompliance and being incompatible with other MTQP implementations.

See also:
 * Message tracking and recall
 * Message tracking MTA options