evpBytesToKey equal openssl EVP_BytesToKey func

evpBytesToKey.swift

    func evpBytesToKey(password:String, keyLen:Int) ->NSData {
        let  md5Len:Int = 16
        
        let cnt = 1// (keyLen -1)/md5Len + 1
        let m = NSMutableData.init(length: cnt*md5Len)!
        let bytes = password.dataUsingEncoding(NSUTF8StringEncoding, allowLossyConversion: false)!
        // memcpy((m?.mutableBytes)!, bytes.bytes , password.characters.count)
        let md5 = bytes.md5
        m.setData(md5)
        
        
        // Repeatedly call md5 until bytes generated is enough.
        // Each call to md5 uses data: prev md5 sum + password.
        let d = NSMutableData.init(length: md5Len+bytes.length)!
        //d := make([]byte, md5Len+len(password))
        var start = 0
        for _ in 0 ..< cnt {
            start += md5Len
            memcpy(d.mutableBytes,m.bytes , m.length)
            memcpy(d.mutableBytes+md5Len, bytes.bytes, bytes.length)
            let md5 = d.md5
            m.appendData(md5)
        }
        
        
        return m
    }

refer https://github.com/shadowsocks/shadowsocks-go/blob/master/shadowsocks/encrypt.go