In this chapter, we have tried to survey the entire huge field of encryption and hashing algorithms available to PHP programmers.
We began by defining first encryption (both symmetric and asymmetric) and then hashing, and then we discussed algorithm strength.
The heart of the chapter was a survey of a whole series of algorithms, first for encryption (both symmetric and asymmetric), next for hashing, and finally for two related algorithms that are unsuitable for serious use. We tried in every case to give some sense of the history of an algorithm, its methods, and its availability.
After a discussion of random numbers, we turned to three other concepts involved in encryption: streams and blocks, modes, and initialization vectors. Finally, we touched on the important issue of governmental oversight over the use and export of encryption algorithms.
This chapter was groundwork for Chapter 6, where we will show how to put the best of the algorithms described here to practical use.
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