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TR-31

A Go library implementing the TR-31 (ANSI X9.143) key block standard for secure cryptographic key exchange.

Overview

TR-31 is a method defined by ASC X9.143 for secure cryptographic key exchange between devices and systems, particularly in the financial industry. This format provides a structured way to protect sensitive key material while maintaining essential metadata about key usage, algorithms, and other attributes.

Project Status

moov-io/tr31 is undergoing active development and testing within Moov. Please star the project and share feedback, bugs, questions, etc in the tr31 channel in slack. If you find security vulnerabilities reach out to [email protected].

Features

• Supports all major TR-31 key block versions:
  • Version A (TDES variant)
  • Version B (TDES key derivation - preferred TDES implementation)
  • Version C (TDES variant)
  • Version D (AES key derivation)
• Implements multiple encryption algorithms:
  • Triple DES (TDES)
  • Single DES (legacy)
  • AES
• Comprehensive error handling with detailed error messages
• Thread-safe operations
• No external dependencies

Installation

go get github.com/moov-io/tr31

Usage

Basic Example

package main

import (
    "fmt"
    "github.com/moov-io/tr31/pkg/tr31"
)

func main() {
    // Create a new header with TR-31 version B
    header, err := encryption.NewHeader(
      encryption.TR31_VERSION_D, // Version ID
      "B0",                      // Key Usage (Data Encryption Key)
      "A",                       // Algorithm (AES)
      "E",                       // Mode of Use (Encrypt)
      "01",                      // Version Number
      "X",                       // Exportability (Exportable with restrictions)
    )

    if err != nil {
        panic(err)
    }

    // Create a key block with your Key Block Protection Key (KBPK)
    kbpkopts := KBPKOptions{
		  Version:   "D",
		  KeyLength: 32,
	  }
    kbpk, _ := GenerateKBPK(kbpkopts)
    // Create a new KeyBlock
    keyBlock, err := encryption.NewKeyBlock(kbpk, header)
    if err != nil {
        panic(err)
    }

    // Wrap a key
    keyToWrap := []byte{...} // Your key to wrap
    wrappedKey, err := keyBlock.Wrap(keyToWrap, nil)
    if err != nil {
        panic(err)
    }

    // Unwrap a key
    unwrappedKey, err := keyBlock.Unwrap(wrappedKey)
    if err != nil {
        panic(err)
    }
}

API Reference

KeyBlock Functions

Wrap

func (kb *KeyBlock) Wrap(key []byte, maskedKeyLen *int) (string, error)

Wraps a cryptographic key using the TR-31 format.

Parameters:

• key: The key to be wrapped (byte slice)
• maskedKeyLen: Optional pointer to an integer specifying the masked key length. If nil, uses the maximum key size for the algorithm.

Returns:

• string: The wrapped key block in TR-31 format
• error: Any error that occurred during the wrapping process

Unwrap

func (kb *KeyBlock) Unwrap(keyBlock string) ([]byte, error)

Unwraps a TR-31 formatted key block to retrieve the original key.

Parameters:

• keyBlock: The TR-31 formatted key block string to unwrap

Returns:

• []byte: The unwrapped key
• error: Any error that occurred during the unwrapping process

Version-Specific Implementation Details

The library supports different TR-31 versions with specific characteristics:

• Version A/C:

  • Uses TDES encryption
  • Simple key derivation (XOR with constants)
  • 4-byte MAC

• Version B:

  • Uses TDES encryption
  • CMAC-based key derivation
  • 8-byte MAC
  • Recommended for TDES implementations

• Version D:

  • Uses AES encryption
  • CMAC-based key derivation
  • 16-byte MAC
  • Supports AES-128, AES-192, and AES-256

Security Considerations

• Always use strong, random Key Block Protection Keys (KBPK)
• Version B is preferred over Version A/C for TDES implementations
• Version D (AES) is recommended for new implementations
• The library performs key length validation and padding automatically
• Ensure your Go environment and dependencies are up to date

Error Handling

The library provides detailed error messages through two custom error types:

• HeaderError: For issues related to TR-31 header processing
• KeyBlockError: For issues related to key block processing

Benchmarks

Unwraps a TR-31 formatted key block to retrieve the original key.

Running tool: /opt/homebrew/bin/go test -benchmem -run=^$ -bench ^BenchmarkUnwrap_D_32_WithSetup$ github.com/moov-io/tr31/pkg/tr31

goos: darwin
goarch: arm64
pkg: github.com/moov-io/tr31/pkg/tr31
cpu: Apple M1 Pro
BenchmarkUnwrap_D_32_WithSetup-10    	  301116	      3619 ns/op	    8608 B/op	      64 allocs/op

Command Line Usage

tr31 is a tool for managing both 3DES and AES-derived unique keys per transaction (TR-31) key management.

USAGE

tr31 [-v] [-algorithm] [-e] [-d]

EXAMPLES

tr31 -v
  Print the version of tr31 (Example: v1.0.0)
tr31 -e
  Encrypt a card data block using the TR-31 transaction key
tr31 -d
  Decrypt a card data block using the TR-31 transaction key

FLAGS

-vault_address string
  Vault address where the encryption/decryption key is stored
-vault_token string
  Vault token for authentication
-key_path string
  Path to the encryption/decryption key in the vault
-key_name string
  Name of the encryption/decryption key in the vault
-wrapper_key string
  Symmetric key
-key_block string
  Wrapped key block for decryption

EXAMPLES

      tr31 -e -vault_address="https://vault-cluster....com:8200" -vault_token="hvs.CA******Ak" -key_path="kv/.../key" -key_name="wrapper_key" -wrapper_key="A0088******A356E"
      tr31 -d -vault_address="https://vault-cluster....com:8200" -vault_token="hvs.CA******Ak" -key_path="kv/.../key" -key_name="kbkp" -key_block="A0088******A356E"

Rest APIs

TR31 library provided web server. Please check following http endpoints

Method	Request Body	Route	Action
POST	JSON	/encrypt_data	Encrypt Data
POST	JSON	/decrypt_data	Decrypt Data

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.

References

• ASC X9.143 Standard
• ANSI TR-31 Documentation

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Note: This implementation is provided as-is. Users should verify the implementation meets their security requirements before using in production environments.