C#版本的OpenSSL EVP_BytesToKey方法？

Question

我正在寻找OpenSSL EVP_BytesToKey函数的直接.NET实现.我发现的最接近的是System.Security.Cryptography.PasswordDeriveBytes类(和Rfc2898DeriveBytes),但它似乎略有不同,并且不生成与EVP_BytesToKey 相同的密钥和iv.

我也发现这个实现似乎是一个好的开始,但没有考虑迭代计数.

我意识到有OpenSSL.NET,但它只是本机openssl DLL的包装,而不是"真正的".NET实现.

Answer 1

我找到了EVP_BytesToKey方法的伪代码解释(在openssl源代码的/doc/ssleay.txt中):

/* M[] is an array of message digests
 * MD() is the message digest function */
M[0]=MD(data . salt);
for (i=1; i<count; i++) M[0]=MD(M[0]);

i=1
while (data still needed for key and iv)
    {
    M[i]=MD(M[i-1] . data . salt);
    for (i=1; i<count; i++) M[i]=MD(M[i]);
    i++;
    }

If the salt is NULL, it is not used.
The digests are concatenated together.
M = M[0] . M[1] . M[2] .......

所以基于此我能够提出这种C#方法(这似乎适用于我的目的并假设32字节密钥和16字节iv):

private static void DeriveKeyAndIV(byte[] data, byte[] salt, int count, out byte[] key, out byte[] iv)
{
    List<byte> hashList = new List<byte>();
    byte[] currentHash = new byte[0];

    int preHashLength = data.Length + ((salt != null) ? salt.Length : 0);
    byte[] preHash = new byte[preHashLength];

    System.Buffer.BlockCopy(data, 0, preHash, 0, data.Length);
    if (salt != null)
        System.Buffer.BlockCopy(salt, 0, preHash, data.Length, salt.Length);

    MD5 hash = MD5.Create();
    currentHash = hash.ComputeHash(preHash);          

    for (int i = 1; i < count; i++)
    {
        currentHash = hash.ComputeHash(currentHash);            
    }

    hashList.AddRange(currentHash);

    while (hashList.Count < 48) // for 32-byte key and 16-byte iv
    {
        preHashLength = currentHash.Length + data.Length + ((salt != null) ? salt.Length : 0);
        preHash = new byte[preHashLength];

        System.Buffer.BlockCopy(currentHash, 0, preHash, 0, currentHash.Length);
        System.Buffer.BlockCopy(data, 0, preHash, currentHash.Length, data.Length);
        if (salt != null)
            System.Buffer.BlockCopy(salt, 0, preHash, currentHash.Length + data.Length, salt.Length);

        currentHash = hash.ComputeHash(preHash);            

        for (int i = 1; i < count; i++)
        {
            currentHash = hash.ComputeHash(currentHash);
        }

        hashList.AddRange(currentHash);
    }
    hash.Clear();
    key = new byte[32];
    iv = new byte[16];
    hashList.CopyTo(0, key, 0, 32);
    hashList.CopyTo(32, iv, 0, 16);
}

更新:这里有更多/更少相同的实现,但使用.NET DeriveBytes接口:https://gist.github.com/1339719

OpenSSL 1.1.0c改变了一些内部组件中使用的摘要算法.以前使用MD5,1.1.0切换到SHA256.请注意,更改不会影响您EVP_BytesToKey和命令openssl enc.