AppSignatureHelper.kt

class AppSignatureHelper(context: Context) : ContextWrapper(context) {

        /**
         * Get all the app signatures for the current package
         * @return
         */
        // Get all package signatures for the current package
        // For each signature create a compatible hash

        fun getAppSignatures(): ArrayList<String> {
            val appCodes = ArrayList<String>()

            try {
                val packageName = packageName
                val packageManager = packageManager
                val signatures = packageManager.getPackageInfo(packageName,
                        PackageManager.GET_SIGNATURES).signatures
                for (signature in signatures) {
                    val hash = hash(packageName, signature.toCharsString())
                    if (hash != null) {
                        appCodes.add(String.format("%s", hash))
                    }
                }
            } catch (e: PackageManager.NameNotFoundException) {
                Log.e(TAG, "Unable to find package to obtain hash.", e)
            }

            return appCodes
        }

        private fun hash(packageName: String, signature: String): String? {
            val appInfo = "$packageName $signature"
            try {
                val messageDigest = MessageDigest.getInstance(HASH_TYPE)
                messageDigest.update(appInfo.toByteArray(StandardCharsets.UTF_8))

                var hashSignature = messageDigest.digest()

                // truncated into NUM_HASHED_BYTES
                hashSignature = Arrays.copyOfRange(hashSignature, 0, NUM_HASHED_BYTES)
                // encode into Base64
                var base64Hash = Base64.encodeToString(hashSignature, Base64.NO_PADDING or Base64.NO_WRAP)
                base64Hash = base64Hash.substring(0, NUM_BASE64_CHAR)

                Log.d(TAG, String.format("pkg: %s -- hash: %s", packageName, base64Hash))
                return base64Hash
            } catch (e: NoSuchAlgorithmException) {
                Log.e(TAG, "hash:NoSuchAlgorithm", e)
            }

            return null
        }
    }