3DES decryption with SHA1 hashed key

Question

Hello all,
I've been given the task of rewriting an existing VB application in Java, and one routine makes use of the Microsoft Cryptography API.
The VB code decrypts a string using TripleDES decryption, using a string key that's been hashed with a SHA1 has algorithm.
Most of the java DESede encryption/decryption examples I've worked through generate keys with a KeyGenerator instance, but I have not yet found any examples that use a key that's been SHA1 hashed.
My attempts at using a hashed byte[] array of my key phrase with a DESede Crypto instance always return a "wrong key size" error.
Can anyone provide some help? Example code fragments or anything would help.

Answer 1

Thanks for the reply, and you're right in that this might be a more appropriate question to ask on a VB forum or on a MS cryptography API forum.
Nevertheless, I've been able to make some headway on the VB side by getting the bytes of the SHA-1 hash map through some API calls.
The hex representation of the SHA-1 hashed keyword:
"3EC10CE885353DCD23B912860C2B91885CD3D6D1"
A keyword to use as a test:
"logins"
Hex representation of the 3DES encrypted result of "logins" using the hashed keyword:
"FB158A921E3C4CDB"
Currently, my problem is with the length of the key. As you pointed out, SHA is 20 bytes, while 3DES is looking for 24 bytes. I'll experiment with your suggested 2-key approach, but here's my test code at the moment:
import java.security.*;
import javax.crypto.*;
import javax.crypto.Cipher;
import javax.crypto.Mac;
import javax.crypto.SecretKey;
import javax.crypto.spec.DESedeKeySpec;
import javax.crypto.spec.SecretKeySpec;
public class EncryptionTest {
public static void main(String[] args) {
String hashedKey = "3EC10CE885353DCD23B912860C2B91885CD3D6D1";
String textToCode = "logins";
byte[] keyBytes = hexStringToBytes( hashedKey );
byte[] source = textToCode.getBytes();
SecretKey key = new SecretKeySpec(keyBytes, "DESede");
try {
Cipher cipher = Cipher.getInstance("DESede");
cipher.init(Cipher.ENCRYPT_MODE, key);
byte[] result = cipher.doFinal(source);
String sresult = hex( result );
System.out.println( result );
} catch ( NoSuchPaddingException e ) {
e.printStackTrace();
} catch ( BadPaddingException e ) { 
e.printStackTrace();
} catch ( NoSuchAlgorithmException e ) {
e.printStackTrace();
} catch ( InvalidKeyException e ) {
e.printStackTrace();
} catch (IllegalBlockSizeException e ) {
e.printStackTrace();
static byte[] hexStringToBytes( String s ) {
int iLength = s.length();
int iBuff = iLength / 2;
byte[] buff = new byte[ iBuff ];
int j = 0;
for(int i = 0; i < iLength; i+=2) {
try {
String s1 = s.substring(i, i+2);
buff[j++] = (byte) Integer.parseInt(s1, 16);
} catch ( Exception e ) {
e.printStackTrace();
return buff;
static String hex(byte[] data) {
StringBuilder sb = new StringBuilder();
for (byte b : data) {
sb.append(Character.forDigit((b & 240) >> 4, 16));
sb.append(Character.forDigit((b & 15), 16));
return sb.toString();
}