Any "out of band" hashes in MD* or SHA-*?

Question

Do any of the common hash algorithms define an "out of band" hash code, i.e. one that is guaranteed to never be the result of the algorithm?

Answer 1

Neither the MD* or SHA-* family of algorithms has an out of band hash value.

If you wish to implement this yourself, you can use the following logic:

• select a random hash value to be the out of band value.
• compute the hash.
• if the hash value (improbably) turns out to be the out of band hash value, assign another hash value.

In pseudocode:

OutOfBandHash = 0xdeadbeefdeadbeefdeadbeefdeadbeef
h = hash(stuff)
if h = OutOfBandHash
    h = OutOfBandHash + 1