Nothing up my sleeve number

Nothing up my sleeve numbers are the the opposite extreme of Chaitin-Kolmogorov randomness in that they appear to be random by statistical tests but are created with minimum entropy. They are typically used in creating cryptographic functions such as hashes and ciphers. These algorithms often need randomized constants for mixing or initialization purposes. The cryptographer may wish to pick these values in a way that demonstrates the constants were not selected for (in B. Schneier's words) a "nefarious reason," for example, to create a "backdoor" to the algorithm. These fears can be allayed by using numbers created in a way that leaves little room for adjustment.

Examples

• The U.S. Government's 1975 Data Encryption Standard came under criticism because no explanation was supplied for the constants used in its S-box.
• Khafre includes constants from the book A Million Random Digits with 100,000 Normal Deviates, published by the RAND Corporation.
• Ron Rivest used the trigonometric sine function to generate constants for MD5.
• The U.S. National Security Agency used the square roots of small integers to produce the constants used in SHA1.
• Others have suggested using the digits of Pi.

Reference

Bruce Schneier, Applied Cryptography, second edition, John Wiley and Sons, 1996