Problem - Kevin Tafuro

Discussion
As a reminder, use a raw mode only if you really know what you’re
doing. For general-purpose use, we recommend a high-level abstraction,
such as that discussed in Recipe 5.16. Additionally, be sure to
include some sort of integrity validation whenever encrypting, as we
discuss throughout Chapter 6.
The signatures for the encryption and decryption routines are identical, and the
actual routines are completely symmetric. Therefore, we’ll only discuss the behavior
of the encryption functions, and you can infer the behavior of the decryption functions
from that.
EVP_EncryptUpdate( ) has the following arguments:
ctx
Pointer to the cipher context previously initialized with EVP_EncryptInit_ex( ).
out
Buffer into which any output is placed.
outl
Pointer to an integer, into which the number of bytes written to the output
buffer is placed.
in
Buffer containing the data to be encrypted.
inl
Number of bytes contained in the input buffer.
EVP_EncryptFinal_ex( ) takes the following arguments:
ctx
Pointer to the cipher context previously initialized with EVP_EncryptInit_ex( ).
out
Buffer into which any output is placed.
outl
Pointer to an integer, into which the number of bytes written to the output
buffer is placed.
There are two phases to encryption in OpenSSL: update, and finalization. The basic
idea behind update mode is that you’re feeding in data to encrypt, and if there’s
incremental output, you get it. Calling the finalization routine lets OpenSSLknow
that all the data to be encrypted with this current context has already been given to
the library. OpenSSLthen does any cleanup work necessary, and it will sometimes
produce additional output. After a cipher is finalized, you need to reinitialize it if you
plan to reuse it, as described in Recipe 5.17.
Performing Low-Level Encryption and Decryption with OpenSSL | 231
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