If you are looking for a free book about applied cryptography, in my opinion this is the best you can find:<p><a href="https:&#x2F;&#x2F;crypto.stanford.edu&#x2F;~dabo&#x2F;cryptobook&#x2F;" rel="nofollow">https:&#x2F;&#x2F;crypto.stanford.edu&#x2F;~dabo&#x2F;cryptobook&#x2F;</a>