Handbook of Applied Cryptography (Discrete Mathematics and Its Applications) by Alfred J. Menezes, Paul C. van Oorshot & Scott A. Vanstone.
ISBN = 0-8493-8523-7

Whereas Schneier’s ‘Applied Cryptography’ reads sometimes like a mystery, this book reads, well, like a handbook. It is for reference not for curling up with. It does have many good and scarce descriptions of crypto relevant info, especially algorithms.

It was my source for testing for irreducible polynomials over Galois fields
and the Jacobi symbol.

See Errata.