LibTomCrypt is a fairly comprehensive, modular and portable
cryptographic toolkit that provides developers with a vast array
of well known published block ciphers, one-way hash functions,
chaining modes, pseudo-random number generators, public key
cryptography and a plethora of other routines.  LibTomCrypt has
been designed from the ground up to be very simple to use. It has
a modular and standard API that allows new ciphers, hashes and PRNGs
to be added or removed without change to the overall end application.
It features easy to use functions and a complete user manual which
has many source snippet examples.

Homepage:
https://www.libtom.net/LibTomCrypt/
