crypto.md

openssl/evp.h - Enveleope Cryptography

The openssl/evp.h header provides a high-level interface to cryptographic functions.

Facilities Overview

Facility Category	Key Symbols	Description
Message Digests	EVP_MD_CTX_new, EVP_DigestInit	Calculating hashes (SHA256, MD5, etc.).
Encryption	EVP_CIPHER_CTX_new, EVP_EncryptInit	Symmetric encryption (AES, etc.).
Public Key	EVP_PKEY_new, EVP_SignInit	Asymmetric cryptography and signatures.

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Types & Variables

EVP_MD_CTX

Context object for message digest (hash) operations.

EVP_CIPHER_CTX

Context object for symmetric cipher operations.

EVP_PKEY

Structure representing a public or private key.

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Functions

Message Digests (Hashing)

EVP_DigestInit_ex

int EVP_DigestInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl)

Initializes the digest context ctx to use type.

Example:

#include <openssl/evp.h>
#include <stdio.h>

int main(void) {
    EVP_MD_CTX *ctx = EVP_MD_CTX_new();
    const EVP_MD *md = EVP_sha256();
    unsigned char hash[EVP_MAX_MD_SIZE];
    unsigned int len;

    EVP_DigestInit_ex(ctx, md, NULL);
    EVP_DigestUpdate(ctx, "Hello", 5);
    EVP_DigestFinal_ex(ctx, hash, &len);

    for(int i = 0; i < len; i++) printf("%02x", hash[i]);
    printf("\n");

    EVP_MD_CTX_free(ctx);
    return 0;
}

EVP_DigestUpdate

int EVP_DigestUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt)

EVP_DigestFinal_ex

int EVP_DigestFinal_ex(EVP_MD_CTX *ctx, unsigned char *md, unsigned int *s)

Symmetric Encryption

EVP_EncryptInit_ex

int EVP_EncryptInit_ex(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *type, ...)