Add Go version of DDP example

ddp_example.go

@@ -0,0 +1,103 @@
+// Dynamic decryption procedure example - (c) 2005 - 2006 Omar A. Herrera Reyna
+// This code is released under GNU General Public License v3.0
+//
+// The following Go program illustrates an implementation of a DDP.
+// It mirrors the original C example but uses Go's standard libraries.
+// The encrypted payload is decrypted only when the key derived from
+// the current UTC hour, month and year matches the expected value.
+// When successful, the program prints the decrypted bytes.
+// Note: Executing the decrypted bytes as code is not included here.
+
+package main
+
+import (
+	"crypto/cipher"
+	"crypto/md5"
+	"encoding/hex"
+	"fmt"
+	"golang.org/x/crypto/blowfish"
+	"time"
+)
+
+const (
+	scodeSize = 172 + 8
+)
+
+var (
+	keyXOR   = [8]byte{0x0F, 0x20, 0x6A, 0x04, 0x10, 0x0D, 0x6E, 0x08}
+	scodeMD5 = [16]byte{0x81, 0xED, 0xD3, 0x62, 0xC6, 0xE3, 0x89, 0x4F,
+		0xD5, 0xA5, 0x6C, 0x95, 0xCE, 0x55, 0x25, 0xE0}
+	encryptedPayload = []byte{
+		0xD7, 0x5A, 0x9A, 0x75, 0x12, 0x8C, 0x44, 0xC0, 0xC3, 0xEB, 0xBC, 0x32, 0x86, 0xD8, 0xB2, 0xD4,
+		0xAF, 0xB6, 0x36, 0xB4, 0x24, 0x4D, 0x7F, 0x2F, 0x6D, 0x70, 0x32, 0xA7, 0xDD, 0xCC, 0xAB, 0x0C,
+		0x5F, 0x9E, 0x79, 0x26, 0x70, 0xA5, 0x6F, 0xAC, 0xB4, 0xB6, 0x71, 0x13, 0xBE, 0xDB, 0xDA, 0x0F,
+		0xAD, 0x1C, 0x10, 0x8D, 0x31, 0x18, 0x34, 0x5E, 0xEA, 0x74, 0xC7, 0xD2, 0x55, 0x86, 0xB8, 0xFA,
+		0x40, 0x47, 0x0E, 0x78, 0xA5, 0xAB, 0x45, 0x8E, 0x08, 0x0C, 0xDA, 0x68, 0xD6, 0x42, 0x54, 0x99,
+		0xE6, 0x54, 0xA1, 0xFC, 0x48, 0xAB, 0xBA, 0x9E, 0x62, 0x6D, 0x52, 0x3C, 0x49, 0xCA, 0x2A, 0xAB,
+		0x63, 0x0B, 0xCD, 0x1A, 0x3C, 0xF7, 0x15, 0x2E, 0xB1, 0x4D, 0x15, 0x11, 0xEA, 0x78, 0x27, 0x3B,
+		0x33, 0x81, 0xD3, 0x9D, 0x8D, 0x9B, 0xE7, 0xBB, 0x0C, 0xC5, 0x97, 0x8C, 0x8E, 0x38, 0x49, 0xE7,
+		0xFD, 0xAB, 0x13, 0x28, 0x9F, 0x45, 0xAC, 0x1C, 0xE0, 0x62, 0xC3, 0x82, 0x47, 0xB8, 0x4A, 0xA3,
+		0xB0, 0x14, 0x2C, 0xFA, 0xC4, 0xE1, 0x51, 0x6A, 0x15, 0x77, 0xDF, 0xA0, 0x3F, 0x24, 0x98, 0x36,
+		0x7B, 0x2D, 0xC2, 0x22, 0x82, 0x76, 0x9A, 0xBC, 0x81, 0xBF, 0x09, 0x01, 0x9C, 0xBE, 0xB2, 0x54,
+		0xEB, 0xF2, 0xFC, 0x7D, 0xD1, 0x77, 0x44, 0xDB, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	}
+)
+
+func deriveKey(t time.Time) [8]byte {
+	var keyTime [8]byte
+	keyTime[0] = byte(t.Hour())
+	keyTime[1] = byte(t.Month() - 1) // tm_mon is 0-based
+	year := t.Year() - 1900          // tm_year is years since 1900
+	keyTime[2] = byte(year)
+	keyTime[3] = byte(year >> 8)
+	keyTime[4] = keyTime[0]
+	keyTime[5] = keyTime[1]
+	keyTime[6] = keyTime[2]
+	keyTime[7] = keyTime[3]
+
+	var key [8]byte
+	for i := 0; i < 8; i++ {
+		key[i] = keyTime[i] ^ keyXOR[i]
+	}
+	return key
+}
+
+func decryptPayload(key [8]byte) ([]byte, error) {
+	block, err := blowfish.NewCipher(key[:])
+	if err != nil {
+		return nil, err
+	}
+	decrypted := make([]byte, len(encryptedPayload))
+	iv := make([]byte, blowfish.BlockSize)
+	mode := cipher.NewCBCDecrypter(block, iv)
+	paddedLen := ((scodeSize + blowfish.BlockSize - 1) / blowfish.BlockSize) * blowfish.BlockSize
+	buf := make([]byte, paddedLen)
+	copy(buf, encryptedPayload[:scodeSize])
+	mode.CryptBlocks(decrypted[:paddedLen], buf)
+	copy(decrypted[paddedLen:], encryptedPayload[paddedLen:])
+	return decrypted, nil
+}
+
+func main() {
+	var decrypted []byte
+	for {
+		time.Sleep(10 * time.Second)
+		key := deriveKey(time.Now().UTC())
+		d, err := decryptPayload(key)
+		if err != nil {
+			fmt.Println("decrypt error:", err)
+			continue
+		}
+		hash := md5.Sum(d[8:scodeSize])
+		if hash == scodeMD5 {
+			decrypted = d
+			fmt.Printf("CORRECT KEY = %X\n", key)
+			break
+		}
+	}
+
+	fmt.Println("Encrypted payload:")
+	fmt.Println(hex.Dump(encryptedPayload))
+	fmt.Println("Decrypted payload:")
+	fmt.Println(hex.Dump(decrypted[8:]))
+}

go.mod

@@ -0,0 +1,5 @@
+module ddp
+
+go 1.23.8
+
+require golang.org/x/crypto v0.39.0

go.sum

@@ -0,0 +1,2 @@
+golang.org/x/crypto v0.39.0 h1:SHs+kF4LP+f+p14esP5jAoDpHU8Gu/v9lFRK6IT5imM=
+golang.org/x/crypto v0.39.0/go.mod h1:L+Xg3Wf6HoL4Bn4238Z6ft6KfEpN0tJGo53AAPC632U=