Problem - Kevin Tafuro

To get the length of the initialization vector:
int EVP_CIPHER_CTX_iv_length(EVP_CIPHER_CTX *ctx);
To get the cipher mode being used:
int EVP_CIPHER_CTX_mode(EVP_CIPHER_CTX *ctx);
To see if automatic padding is disabled:
int pad = (ctx->flags & EVP_CIPH_NO_PADDING);
To see if we are encrypting or decrypting:
int encr = (ctx->encrypt);
To retrieve the original initialization vector:
char *iv = (ctx->oiv);
Discussion
The EVP_CIPHER_CTX_cipher( ) function is actually implemented as a macro that
returns an object of type EVP_CIPHER. The cipher itself can be queried, but interesting
queries can also be made on the context object through appropriate macros.
All functions returning lengths return them in bytes.
The EVP_CIPHER_CTX_mode( ) function returns one of the following predefined values:
EVP_CIPH_ECB_MODE
EVP_CIPH_CBC_MODE
EVP_CIPH_CFB_MODE
EVP_CIPH_OFB_MODE
5.22 Performing Low-Level Encryption and
Decryption with OpenSSL
Problem
You have set up your cipher and want to perform encryption and decryption.
Solution
Use the following suite of functions:
int EVP_EncryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl);
int EVP_EncryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
int EVP_DecryptUpdate(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl,
unsigned char *in, int inl);
int EVP_DecryptFinal_ex(EVP_CIPHER_CTX *ctx, unsigned char *out, int *outl);
230 | Chapter 5: Symmetric Encryption
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