For example, the command:
openssl enc -aes-256-cbc -a -in test.txt -k pinkrhino -nosalt -p -out openssl_output.txt
outputs something like:
key = 33D890D33F91D52FC9B405A0DDA65336C3C4B557A3D79FE69AB674BE82C5C3D2
iv = 677C95C475C0E057B739750748608A49
How is that key generated? (C code as an answer would be too awesome to ask for :) ) Also, how is the iv generated?
Looks like some kind of hex to me.
OpenSSL 使用函数EVP_BytesToKey。您可以在 中找到对它的调用apps/enc.c。enc如果您没有使用参数指定不同的摘要，则该实用程序在密钥派生算法 (KDF) 中默认使用 MD5 摘要-md。现在它默认使用 SHA-256。这是一个使用 MD5 的工作示例：
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/evp.h>
int main(int argc, char *argv[])
{
const EVP_CIPHER *cipher;
const EVP_MD *dgst = NULL;
unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH];
const char *password = "password";
const unsigned char *salt = NULL;
int i;
OpenSSL_add_all_algorithms();
cipher = EVP_get_cipherbyname("aes-256-cbc");
if(!cipher) { fprintf(stderr, "no such cipher\n"); return 1; }
dgst=EVP_get_digestbyname("md5");
if(!dgst) { fprintf(stderr, "no such digest\n"); return 1; }
if(!EVP_BytesToKey(cipher, dgst, salt,
(unsigned char *) password,
strlen(password), 1, key, iv))
{
fprintf(stderr, "EVP_BytesToKey failed\n");
return 1;
}
printf("Key: "); for(i=0; i<cipher->key_len; ++i) { printf("%02x", key[i]); } printf("\n");
printf("IV: "); for(i=0; i<cipher->iv_len; ++i) { printf("%02x", iv[i]); } printf("\n");
return 0;
}
示例用法：
gcc b2k.c -o b2k -lcrypto -g
./b2k
Key: 5f4dcc3b5aa765d61d8327deb882cf992b95990a9151374abd8ff8c5a7a0fe08
IV: b7b4372cdfbcb3d16a2631b59b509e94
它生成与此 OpenSSL 命令行相同的密钥：
openssl enc -aes-256-cbc -k password -nosalt -p < /dev/null
key=5F4DCC3B5AA765D61D8327DEB882CF992B95990A9151374ABD8FF8C5A7A0FE08
iv =B7B4372CDFBCB3D16A2631B59B509E94
OpenSSL 1.1.0c 更改了一些内部组件中使用的摘要算法。以前使用MD5，1.1.0改用SHA256。请注意，更改不会影响您EVP_BytesToKey和openssl enc.
如果有人通过这里正在寻找在 Haskell 中工作的、高性能的参考实现，这里是：
import Crypto.Hash
import qualified Data.ByteString as B
import Data.ByteArray (convert)
import Data.Monoid ((<>))
evpBytesToKey :: HashAlgorithm alg =>
Int -> Int -> alg -> Maybe B.ByteString -> B.ByteString -> (B.ByteString, B.ByteString)
evpBytesToKey keyLen ivLen alg mSalt password =
let bytes = B.concat . take required . iterate go $ hash' passAndSalt
(key, rest) = B.splitAt keyLen bytes
in (key, B.take ivLen rest)
where
hash' = convert . hashWith alg
required = 1 + ((keyLen + ivLen - 1) `div` hashDigestSize alg)
passAndSalt = maybe password (password <>) mSalt
go = hash' . (<> passAndSalt)
它使用cryptonite包提供的哈希算法。参数是所需的密钥和 IV 大小（以字节为单位）、要使用的哈希算法（例如(undefined :: MD5)）、可选的盐和密码。结果是 key 和 IV 的元组。
如果有人正在寻找在 SWIFT 中实现相同的功能，我将EVP_BytesToKey在 swift中进行转换
/*
- parameter keyLen: keyLen
- parameter ivLen: ivLen
- parameter digest: digest e.g "md5" or "sha1"
- parameter salt: salt
- parameter data: data
- parameter count: count
- returns: key and IV respectively
*/
open static func evpBytesToKey(_ keyLen:Int, ivLen:Int, digest:String, salt:[UInt8], data:Data, count:Int)-> [[UInt8]] {
let saltData = Data(bytes: UnsafePointer<UInt8>(salt), count: Int(salt.count))
var both = [[UInt8]](repeating: [UInt8](), count: 2)
var key = [UInt8](repeating: 0,count: keyLen)
var key_ix = 0
var iv = [UInt8](repeating: 0,count: ivLen)
var iv_ix = 0
var nkey = keyLen;
var niv = ivLen;
var i = 0
var addmd = 0
var md:Data = Data()
var md_buf:[UInt8]
while true {
addmd = addmd + 1
md.append(data)
md.append(saltData)
if(digest=="md5"){
md = NSData(data:md.md5()) as Data
}else if (digest == "sha1"){
md = NSData(data:md.sha1()) as Data
}
for _ in 1...(count-1){
if(digest=="md5"){
md = NSData(data:md.md5()) as Data
}else if (digest == "sha1"){
md = NSData(data:md.sha1()) as Data
}
}
md_buf = Array (UnsafeBufferPointer(start: md.bytes, count: md.count))
// md_buf = Array(UnsafeBufferPointer(start: md.bytes.bindMemory(to: UInt8.self, capacity: md.count), count: md.length))
i = 0
if (nkey > 0) {
while(true) {
if (nkey == 0){
break
}
if (i == md.count){
break
}
key[key_ix] = md_buf[i];
key_ix = key_ix + 1
nkey = nkey - 1
i = i + 1
}
}
if (niv > 0 && i != md_buf.count) {
while(true) {
if (niv == 0){
break
}
if (i == md_buf.count){
break
}
iv[iv_ix] = md_buf[i]
iv_ix = iv_ix + 1
niv = niv - 1
i = i + 1
}
}
if (nkey == 0 && niv == 0) {
break
}
}
both[0] = key
both[1] = iv
return both
}
我使用CryptoSwift作为哈希。这是一种更简洁的方式，因为苹果不推荐在 iOS 中使用 OpenSSL
更新：斯威夫特 3
这是 mbedTLS / Polar SSL 的版本 - 经过测试并且可以正常工作。
typedef int bool;
#define false 0
#define true (!false)
//------------------------------------------------------------------------------
static bool EVP_BytesToKey( const unsigned int nDesiredKeyLen, const unsigned char* salt,
const unsigned char* password, const unsigned int nPwdLen,
unsigned char* pOutKey, unsigned char* pOutIV )
{
// This is a re-implemntation of openssl's password to key & IV routine for mbedtls.
// (See openssl apps/enc.c and /crypto/evp/evp_key.c) It is not any kind of
// standard (e.g. PBKDF2), and it only uses an interation count of 1, so it's
// pretty crappy. MD5 is used as the digest in Openssl 1.0.2, 1.1 and late
// use SHA256. Since this is for embedded system, I figure you know what you've
// got, so I made it compile-time configurable.
//
// The signature has been re-jiggered to make it less general.
//
// See: https://wiki.openssl.org/index.php/Manual:EVP_BytesToKey(3)
// And: https://www.cryptopp.com/wiki/OPENSSL_EVP_BytesToKey
#define IV_BYTE_COUNT 16
#if BTK_USE_MD5
# define DIGEST_BYTE_COUNT 16 // MD5
#else
# define DIGEST_BYTE_COUNT 32 // SHA
#endif
bool bRet;
unsigned char md_buf[ DIGEST_BYTE_COUNT ];
mbedtls_md_context_t md_ctx;
bool bAddLastMD = false;
unsigned int nKeyToGo = nDesiredKeyLen; // 32, typical
unsigned int nIVToGo = IV_BYTE_COUNT;
mbedtls_md_init( &md_ctx );
#if BTK_USE_MD5
int rc = mbedtls_md_setup( &md_ctx, mbedtls_md_info_from_type( MBEDTLS_MD_MD5 ), 0 );
#else
int rc = mbedtls_md_setup( &md_ctx, mbedtls_md_info_from_type( MBEDTLS_MD_SHA256 ), 0 );
#endif
if (rc != 0 )
{
fprintf( stderr, "mbedutils_md_setup() failed -0x%04x\n", -rc );
bRet = false;
goto exit;
}
while( 1 )
{
mbedtls_md_starts( &md_ctx ); // start digest
if ( bAddLastMD == false ) // first time
{
bAddLastMD = true; // do it next time
}
else
{
mbedtls_md_update( &md_ctx, &md_buf[0], DIGEST_BYTE_COUNT );
}
mbedtls_md_update( &md_ctx, &password[0], nPwdLen );
mbedtls_md_update( &md_ctx, &salt[0], 8 );
mbedtls_md_finish( &md_ctx, &md_buf[0] );
//
// Iteration loop here in original removed as unused by "openssl enc"
//
// Following code treats the output key and iv as one long, concatentated buffer
// and smears as much digest across it as is available. If not enough, it takes the
// big, enclosing loop, makes more digest, and continues where it left off on
// the last iteration.
unsigned int ii = 0; // index into mb_buf
if ( nKeyToGo != 0 ) // still have key to fill in?
{
while( 1 )
{
if ( nKeyToGo == 0 ) // key part is full/done
break;
if ( ii == DIGEST_BYTE_COUNT ) // ran out of digest, so loop
break;
*pOutKey++ = md_buf[ ii ]; // stick byte in output key
nKeyToGo--;
ii++;
}
}
if ( nIVToGo != 0 // still have fill up IV
&& // and
ii != DIGEST_BYTE_COUNT // have some digest available
)
{
while( 1 )
{
if ( nIVToGo == 0 ) // iv is full/done
break;
if ( ii == DIGEST_BYTE_COUNT ) // ran out of digest, so loop
break;
*pOutIV++ = md_buf[ ii ]; // stick byte in output IV
nIVToGo--;
ii++;
}
}
if ( nKeyToGo == 0 && nIVToGo == 0 ) // output full, break main loop and exit
break;
} // outermost while loop
bRet = true;
exit:
mbedtls_md_free( &md_ctx );
return bRet;
}