Monograph:

Commercial cryptographers have long been concerned with how much execution time their cryptographic implementations require.

The amount of time used to encrypt a message or produce a digital signature is often used as a benchmark when comparing different cryptographic schemes; with all other factors being equal, the fastest scheme is considered the most efficient and is hence the most marketable.

The amount of time it takes to compute a cryptographic function depends not only on what that function does but also what inputs are passed to it. Certain encodings of messages may require less time to encrypt because of the mathematical operations used. For example, an encryption function based on integer multiplication might be quick to evaluate with pen and paper if the message to encrypt is a power of ten.

A prudent cryptographer might then try to express every message as a power of ten to exploit this computational shortcut. However, in addition to messages, cryptographic functions often take secret keys as input and so the value of a key might influence publicly observably timing characteristics.

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