Problematic Relationship of Pt, Ct, and MAC

In one quality problematic encryption example given a chosen key, the
Ct is slightly longer than the Pt. If the Ct is decoded, the Pt
results but if the Pt is treated the same way, decode routine, a hash
slightly shorter than the Pt results. So, if Ct is sent with the hash
of the Pt as a MAC, the proper receiver can show with some relative
comfort that when the Pt he recovers and subsequent double decoding
yields a hash that is the same MAC as received, all is well.

The algorithm used meets neither classical block nor stream cipher
criteria but is in an distinct new class.
.

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