Go SHA-256 hash differs from Java SHA-256 hash

Question

If I generate the SHA-256 hash in the language "GO", I get a different byte-Array compared to the Java equivalent.

This is the GO version:

fmt.Println(getSha256([]byte("5nonce=5")))

The resulting array looks like:

41 79 186 235 199 123 95 226 16 59 51 161 112 245 192 50 21 66 180 250 179 109 153 18 233 148 16 237 156 69 163 150]

This one should do the same in Java code:

MessageDigest md = MessageDigest.getInstance("SHA-256");

md.update("5nonce=5".getBytes()); 
byte[] digest = md.digest();

But results in this byte array

[41, 79, -70, -21, -57, 123, 95, -30, 16, 59, 51, -95, 112, -11, -64, 50, 21, 66, -76, -6, -77, 109, -103, 18, -23, -108, 16, -19, -100, 69, -93, -106]

Why are they different? How do I need to change the java version to work exactly like the Go version?

Answer 1

Why are they different?

They're not, really. They're the same bits. It's just that Java doesn't have unsigned bytes - so any byte with the top bit set is negative. In every case like that, you'll see that Java result = Go result - 256.

If you convert both byte arrays to hex or base64, you'll see same results.

Answer 2

Here is the Go code which would produce the same result:

package main

import "fmt"
import "crypto/sha256"

func main() {
    sum224 := sha256.Sum256([]byte("5nonce=5"))
    s := make([]int8, sha256.Size)
    for i := range sum224 {
        s[i] = int8(sum224[i])
    }
    fmt.Printf("%d", s)
}

[41 79 -70 -21 -57 123 95 -30 16 59 51 -95 112 -11 -64 50 21 66 -76 -6 -77 109 -103 18 -23 -108 16 -19 -100 69 -93 -106]

The fmt doc does mention:

There is no 'u' flag. Integers are printed unsigned if they have unsigned type.

Since Numeric Types defines:

• byte alias for uint8
• uint8 the set of all unsigned 8-bit integers (0 to 255)
• int8 the set of all signed 8-bit integers (-128 to 127)

That is why you would need to convert byte (unsigned) into signed int8 to see the same.

---

If you add base64 encoding (see golang playground), you can get a result easier to compare:

import "encoding/base64"

res := base64.StdEncoding.EncodeToString([]byte(sum224[:]))
fmt.Println(res)

That returns:

KU+668d7X+IQOzOhcPXAMhVCtPqzbZkS6ZQQ7ZxFo5Y=