Returns the length in bytes that an output buffer would need to be in
 order to hold the result of the next
 engineGenExemptionBlob
 operation, given the input length inputLen (in bytes).
 
The actual output length of the next
 engineGenExemptionBlob
 call may be smaller than the length returned by this method.
| inputLen | the input length (in bytes) | 
Diagram: ExemptionMechanism