first commit

internal/interfaces/bpjs/crypto.go

@@ -0,0 +1,58 @@
+package bpjs
+
+import (
+	"crypto/aes"
+	"crypto/cipher"
+	"crypto/sha256"
+	"encoding/base64"
+	"errors"
+)
+
+// DecryptPayload mengembalikan payload BPJS API yang sudah didekripsi dan disalurkan ke mesin dekompresi otomatis.
+func DecryptPayload(cipherText string, consID, secretKey, timestamp string) (string, error) {
+	if cipherText == "" {
+		return "", errors.New("ciphertext cannot be empty")
+	}
+
+	// 1. Generate Key dari gabungan ConsID + SecretKey + Timestamp
+	keyString := consID + secretKey + timestamp
+	hash := sha256.Sum256([]byte(keyString))
+	key := hash[:]
+
+	// IV adalah 16 byte pertama dari key
+	iv := key[:16]
+
+	// 2. Base64 Decode CipherText
+	cipherBytes, err := base64.StdEncoding.DecodeString(cipherText)
+	if err != nil {
+		return "", errors.New("failed to base64 decode cipher text")
+	}
+
+	// 3. AES-256-CBC Decryption
+	block, err := aes.NewCipher(key)
+	if err != nil {
+		return "", err
+	}
+
+	if len(cipherBytes)%aes.BlockSize != 0 {
+		return "", errors.New("ciphertext is not a multiple of the block size")
+	}
+
+	mode := cipher.NewCBCDecrypter(block, iv)
+	mode.CryptBlocks(cipherBytes, cipherBytes)
+
+	// Unpad PKCS7
+	cipherBytes = unpadPKCS7(cipherBytes)
+
+	// 4. Automatis Dekompresi menggunakan Advanced Handler (LZString/Gzip)
+	return DecompressPayload(cipherBytes)
+}
+
+func unpadPKCS7(b []byte) []byte {
+	length := len(b)
+	if length == 0 {
+		return b
+	}
+	unpadding := int(b[length-1])
+	return b[:(length - unpadding)]
+}