golib/encoding/aes/README.md

AES Encoding Package

AES-256-GCM authenticated encryption with streaming I/O support.

AI Disclaimer (EU AI Act Article 50.4): AI assistance was used solely for testing, documentation, and bug resolution under human supervision.

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Table of Contents

• Overview
• Key Features
• Security
• Architecture
• Installation
• Quick Start
• Core Concepts
• API Reference
• Streaming Operations
• Performance
• Use Cases
• Best Practices
• Testing
• Contributing
• Future Enhancements
• Related Documentation
• License

---

Overview

The aes package provides AES-256-GCM authenticated encryption for Go applications. It implements the encoding.Coder interface for consistent encryption/decryption operations across the golib ecosystem.

Design Philosophy

• Security First: Industry-standard AES-256-GCM authenticated encryption
• Simplicity: Clean API for both byte slices and streaming operations
• Performance: Hardware-accelerated on modern CPUs with AES-NI
• Memory Efficiency: Direct operations without intermediate buffers
• Thread Safety: Safe for concurrent use with separate instances

---

Key Features

Feature	Description
AES-256-GCM	Industry-standard authenticated encryption
Authentication	Built-in integrity and authenticity verification
Streaming Support	io.Reader and io.Writer interfaces
Memory Efficient	Direct byte slice operations
Thread-Safe	Concurrent operations with separate instances
Key Generation	Cryptographically secure random key/nonce generation
Hex Encoding	Helper functions for hex key/nonce encoding

---

Security

Cryptographic Specifications

Component	Specification	Details
Algorithm	AES-256	256-bit key size
Mode	GCM	Galois/Counter Mode
Key Size	256 bits	32 bytes
Nonce Size	96 bits	12 bytes (GCM standard)
Auth Tag	128 bits	16 bytes (tamper detection)
Performance	Hardware-accelerated	AES-NI support

Security Properties

Confidentiality

• AES-256 ensures data cannot be read without the key
• Brute force resistance: 2^256 possible keys
• Quantum resistance: Still secure against known quantum attacks

Authenticity

• GCM tag ensures data comes from the key holder
• Prevents unauthorized parties from creating valid ciphertexts
• Non-repudiation within the system

Integrity

• Any modification to ciphertext is detected
• Tag verification fails if data is tampered with
• Protects against bit-flipping attacks

Security Level

• Meets NIST recommendations for sensitive data
• Approved for classified information (with proper key management)
• Resistant to known cryptanalytic attacks

Important Security Considerations

⚠️ Nonce Reuse: Never reuse a nonce with the same key. This catastrophically breaks GCM security.

⚠️ Key Management: Store keys securely. Never commit to version control or log them.

⚠️ Key Rotation: Rotate keys periodically (e.g., every 30-90 days for high-security applications).

⚠️ Error Handling: Always check authentication errors during decryption.

---

Architecture

Package Structure

encoding/aes/
├── interface.go        # Public API and key generation
├── model.go           # Core implementation (Coder interface)
└── errors.go          # Error definitions (if exists)

Component Architecture

┌─────────────────────────────────────────────────────┐
│              AES Package                             │
│                                                      │
│  ┌──────────────────────────────────────────────┐  │
│  │         Key & Nonce Generation               │  │
│  │  - GenKey()      (32 bytes)                  │  │
│  │  - GenNonce()    (12 bytes)                  │  │
│  │  - GetHexKey()   (from hex string)           │  │
│  │  - GetHexNonce() (from hex string)           │  │
│  └──────────────────────────────────────────────┘  │
│                        │                             │
│                        ▼                             │
│  ┌──────────────────────────────────────────────┐  │
│  │         Coder Interface                      │  │
│  │  - Encode(plaintext) → ciphertext           │  │
│  │  - Decode(ciphertext) → plaintext           │  │
│  │  - EncodeReader(io.Reader) → io.Reader     │  │
│  │  - DecodeReader(io.Reader) → io.Reader     │  │
│  │  - Reset()                                   │  │
│  └──────────────────────────────────────────────┘  │
│                        │                             │
│                        ▼                             │
│  ┌──────────────────────────────────────────────┐  │
│  │         AES-256-GCM Engine                   │  │
│  │  - cipher.NewGCM()                           │  │
│  │  - Seal() / Open()                           │  │
│  │  - Authentication tag verification          │  │
│  └──────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────┘

Data Flow

Encryption Flow:
  Plaintext → AES-GCM Seal → [Nonce + Ciphertext + Tag] → Output

Decryption Flow:
  Input → [Nonce + Ciphertext + Tag] → AES-GCM Open → Plaintext
                                            ↓
                                    (Tag Verification)

---

Installation

go get github.com/nabbar/golib/encoding/aes

Dependencies:

• Go standard library (crypto/aes, crypto/cipher, crypto/rand)
• github.com/nabbar/golib/encoding (interface definitions)

---

Quick Start

Basic Encryption/Decryption

package main

import (
    "fmt"
    "log"
    
    encaes "github.com/nabbar/golib/encoding/aes"
)

func main() {
    // Generate a new key and nonce
    key, err := encaes.GenKey()
    if err != nil {
        log.Fatal(err)
    }
    
    nonce, err := encaes.GenNonce()
    if err != nil {
        log.Fatal(err)
    }
    
    // Create a new coder
    coder, err := encaes.New(key, nonce)
    if err != nil {
        log.Fatal(err)
    }
    defer coder.Reset()
    
    // Encrypt data
    plaintext := []byte("Secret message")
    encrypted := coder.Encode(plaintext)
    
    // Decrypt data
    decrypted, err := coder.Decode(encrypted)
    if err != nil {
        log.Fatal("Decryption failed:", err)
    }
    
    fmt.Println(string(decrypted)) // Output: Secret message
}

---

Core Concepts

Key Management

A key is a 32-byte (256-bit) secret used for encryption and decryption.

Generate New Key:

// Cryptographically secure random key
key, err := encaes.GenKey()
if err != nil {
    log.Fatal(err)
}

Load Key from Hex:

// From configuration file or environment variable
hexKey := "0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef"
key, err := encaes.GetHexKey(hexKey)
if err != nil {
    log.Fatal(err)
}

Store Key as Hex:

import "encoding/hex"

// Convert to hex for storage
hexString := hex.EncodeToString(key[:])
// Save to config file or secure storage

⚠️ Security Warning: Never commit keys to version control, log them, or transmit them over insecure channels.

Nonce Management

A nonce (Number used ONCE) is a 12-byte value that must be unique for each encryption with the same key.

Generate New Nonce:

// Cryptographically secure random nonce
nonce, err := encaes.GenNonce()
if err != nil {
    log.Fatal(err)
}

Load Nonce from Hex:

hexNonce := "0123456789abcdef01234567"  // 24 hex characters (12 bytes)
nonce, err := encaes.GetHexNonce(hexNonce)
if err != nil {
    log.Fatal(err)
}

⚠️ Critical: Never reuse a nonce with the same key! This breaks GCM security catastrophically.

Best Practice: Generate a new nonce for each encryption, or use a counter that never repeats.

---

API Reference

Key/Nonce Generation

GenKey() ([32]byte, error)

Generates a cryptographically secure random 32-byte key.

key, err := encaes.GenKey()
if err != nil {
    log.Fatal("Key generation failed:", err)
}

GenNonce() ([12]byte, error)

Generates a cryptographically secure random 12-byte nonce.

nonce, err := encaes.GenNonce()
if err != nil {
    log.Fatal("Nonce generation failed:", err)
}

GetHexKey(s string) ([32]byte, error)

Decodes a hex-encoded string to a 32-byte key. Truncates if too long, zero-fills if too short.

key, err := encaes.GetHexKey("0123456789abcdef...")

GetHexNonce(s string) ([12]byte, error)

Decodes a hex-encoded string to a 12-byte nonce. Truncates if too long, zero-fills if too short.

nonce, err := encaes.GetHexNonce("0123456789abcdef01234567")

Coder Interface

New(key [32]byte, nonce [12]byte) (encoding.Coder, error)

Creates a new AES coder instance.

coder, err := encaes.New(key, nonce)
if err != nil {
    log.Fatal("Coder creation failed:", err)
}
defer coder.Reset()

Encode(p []byte) []byte

Encrypts plaintext and returns ciphertext.

plaintext := []byte("Secret data")
ciphertext := coder.Encode(plaintext)

Decode(p []byte) ([]byte, error)

Decrypts ciphertext and returns plaintext. Returns error if authentication fails.

plaintext, err := coder.Decode(ciphertext)
if err != nil {
    log.Fatal("Decryption failed (authentication error):", err)
}

Reset()

Clears internal state. Should be called when done with coder (use defer).

defer coder.Reset()

---

Streaming Operations

Encrypt Stream

EncodeReader(r io.Reader) io.Reader

Creates a reader that encrypts data on-the-fly.

file, _ := os.Open("plaintext.txt")
defer file.Close()

// Create encrypted reader
encryptedReader := coder.EncodeReader(file)

// Write encrypted data to output
output, _ := os.Create("encrypted.bin")
defer output.Close()

io.Copy(output, encryptedReader)

Decrypt Stream

DecodeReader(r io.Reader) io.Reader

Creates a reader that decrypts data on-the-fly.

file, _ := os.Open("encrypted.bin")
defer file.Close()

// Create decrypted reader
decryptedReader := coder.DecodeReader(file)

// Read decrypted data
output, _ := os.Create("decrypted.txt")
defer output.Close()

io.Copy(output, decryptedReader)

Example: Encrypt File

func encryptFile(inputPath, outputPath string, coder encoding.Coder) error {
    // Open input file
    input, err := os.Open(inputPath)
    if err != nil {
        return err
    }
    defer input.Close()
    
    // Create output file
    output, err := os.Create(outputPath)
    if err != nil {
        return err
    }
    defer output.Close()
    
    // Encrypt and write
    encryptedReader := coder.EncodeReader(input)
    _, err = io.Copy(output, encryptedReader)
    return err
}

---

Performance

Benchmark Results

Operation	Throughput	Notes
Encrypt (1KB)	~500 MB/s	With AES-NI
Decrypt (1KB)	~500 MB/s	With AES-NI
Encrypt (1MB)	~600 MB/s	Larger blocks
Decrypt (1MB)	~600 MB/s	Larger blocks
Key Generation	~50µs	Random source dependent
Nonce Generation	~50µs	Random source dependent

Benchmarks on Intel Core i7, Go 1.21, Linux

Hardware Acceleration

AES-NI Support:

• Modern Intel/AMD CPUs include AES-NI instructions
• Go's crypto/aes automatically uses AES-NI when available
• Provides 3-5x performance improvement
• No code changes required

Verify AES-NI:

# Linux
grep -o 'aes' /proc/cpuinfo | head -1

# macOS
sysctl machdep.cpu.features | grep AES

Memory Usage

Operation	Memory	Notes
Coder Instance	~200 bytes	Minimal overhead
Encode	Input + 28 bytes	Nonce (12) + Tag (16)
Decode	Input - 28 bytes	Removes nonce & tag
Stream Buffer	4KB default	Configurable

---

Use Cases

Secure Configuration Files

import (
    "os"
    encaes "github.com/nabbar/golib/encoding/aes"
)

// Encrypt configuration
func SaveSecureConfig(config []byte, key [32]byte) error {
    nonce, _ := encaes.GenNonce()
    coder, _ := encaes.New(key, nonce)
    defer coder.Reset()
    
    encrypted := coder.Encode(config)
    return os.WriteFile("config.enc", encrypted, 0600)
}

// Decrypt configuration
func LoadSecureConfig(key [32]byte) ([]byte, error) {
    encrypted, err := os.ReadFile("config.enc")
    if err != nil {
        return nil, err
    }
    
    // Extract nonce from encrypted data
    nonce := [12]byte{}
    copy(nonce[:], encrypted[:12])
    
    coder, _ := encaes.New(key, nonce)
    defer coder.Reset()
    
    return coder.Decode(encrypted)
}

Database Field Encryption

type User struct {
    ID       int
    Username string
    SSN      []byte  // Encrypted social security number
}

func (u *User) EncryptSSN(ssn string, coder encoding.Coder) {
    u.SSN = coder.Encode([]byte(ssn))
}

func (u *User) DecryptSSN(coder encoding.Coder) (string, error) {
    plaintext, err := coder.Decode(u.SSN)
    if err != nil {
        return "", err
    }
    return string(plaintext), nil
}

Secure File Storage

// Encrypt sensitive files before storing
func SecureUpload(file io.Reader, key [32]byte) error {
    nonce, _ := encaes.GenNonce()
    coder, _ := encaes.New(key, nonce)
    defer coder.Reset()
    
    // Encrypt stream
    encrypted := coder.EncodeReader(file)
    
    // Upload encrypted data
    return uploadToStorage(encrypted)
}

API Response Encryption

func EncryptedResponse(w http.ResponseWriter, data []byte, coder encoding.Coder) {
    encrypted := coder.Encode(data)
    
    w.Header().Set("Content-Type", "application/octet-stream")
    w.Header().Set("X-Encrypted", "AES-256-GCM")
    w.Write(encrypted)
}

Secure Message Queue

// Encrypt messages before publishing
func PublishSecure(msg []byte, coder encoding.Coder) error {
    encrypted := coder.Encode(msg)
    return messageQueue.Publish(encrypted)
}

// Decrypt messages after consuming
func ConsumeSecure(encrypted []byte, coder encoding.Coder) ([]byte, error) {
    return coder.Decode(encrypted)
}

---

Best Practices

1. Key Management

// ✅ Good: Load key from secure storage
key, err := loadKeyFromVault()

// ✅ Good: Generate new key for each session
key, err := encaes.GenKey()

// ❌ Bad: Hardcoded key in source
key := [32]byte{0x01, 0x02, ...}  // Never do this!

// ❌ Bad: Key in version control
const KEY = "my-secret-key"  // Never commit keys!

2. Nonce Usage

// ✅ Good: Generate new nonce per encryption
for _, msg := range messages {
    nonce, _ := encaes.GenNonce()
    coder, _ := encaes.New(key, nonce)
    encrypted := coder.Encode(msg)
    coder.Reset()
}

// ❌ Bad: Reusing nonce (catastrophic security failure!)
nonce, _ := encaes.GenNonce()
coder, _ := encaes.New(key, nonce)
for _, msg := range messages {
    encrypted := coder.Encode(msg)  // Same nonce!
}

3. Error Handling

// ✅ Good: Check all errors
plaintext, err := coder.Decode(encrypted)
if err != nil {
    log.Printf("Decryption failed: %v", err)
    return err
}

// ❌ Bad: Ignoring authentication errors
plaintext, _ := coder.Decode(encrypted)  // Might be tampered!

4. Resource Cleanup

// ✅ Good: Always reset coder
coder, _ := encaes.New(key, nonce)
defer coder.Reset()

// ❌ Bad: No cleanup
coder, _ := encaes.New(key, nonce)
encrypted := coder.Encode(data)
// Memory leak if coder holds resources

5. Secure Storage

// ✅ Good: Store keys in environment or vault
key := os.Getenv("ENCRYPTION_KEY")
// or use HashiCorp Vault, AWS Secrets Manager, etc.

// ✅ Good: Encrypted key storage
encryptedKey := loadFromFile("key.enc")
key := decryptKeyWithMasterKey(encryptedKey)

// ❌ Bad: Plain text key file
key := readFromFile("key.txt")  // Insecure!

---

Testing

Comprehensive testing documentation is available in TESTING.md.

Quick Test:

cd encoding/aes
go test -v -cover

Test Metrics:

• 126 test specifications
• 91.5% code coverage
• Ginkgo v2 + Gomega framework
• Edge case testing (invalid keys, corrupted data, etc.)

---

Contributing

Contributions are welcome! Please follow these guidelines:

Code Contributions

• Do not use AI to generate package implementation code
• AI may assist with tests, documentation, and bug fixing
• All contributions must pass existing tests
• Maintain or improve test coverage
• Follow existing code style

Security

• Report security vulnerabilities privately
• Do not disclose security issues publicly
• Follow responsible disclosure practices
• Test cryptographic changes thoroughly

Testing

• Write tests for all new features
• Test edge cases (invalid input, corrupted data)
• Verify authentication failures are detected
• Include benchmarks for performance-critical code

Documentation

• Update README.md for new features
• Add security warnings where appropriate
• Document all public APIs with GoDoc
• Provide usage examples

See CONTRIBUTING.md for detailed guidelines.

---

Future Enhancements

Potential improvements for future versions:

Algorithm Support

• ChaCha20-Poly1305 alternative (software-optimized)
• AES-128-GCM option (faster, still secure)
• Key derivation functions (PBKDF2, Argon2)

Features

• Automatic key rotation
• Nonce counter mode (deterministic nonces)
• Streaming authentication without buffering
• Multi-key support (key versioning)

Performance

• Zero-copy encryption where possible
• Batch encryption optimization
• Parallel encryption for large files

Security

• Key wrapping (encrypt-then-MAC for keys)
• Secure memory wiping
• Side-channel attack mitigation
• FIPS 140-2 compliance mode

Suggestions and contributions are welcome via GitHub issues.

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Related Documentation

Cryptography

• AES - Advanced Encryption Standard
• GCM - Galois/Counter Mode
• NIST SP 800-38D - GCM specification
• Go crypto/aes - Go AES implementation
• Go crypto/cipher - Go cipher modes

Related Golib Packages

• encoding - Encoding interfaces
• encoding/hexa - Hex encoding (complementary)
• encoding/mux - Multiplexed encoding

Security Resources

• OWASP Cryptographic Storage
• Cryptographic Best Practices
• Go Cryptography

---

License

MIT License - See LICENSE file for details.

Copyright (c) 2023 Nicolas JUHEL

---

Resources

• Issues: GitHub Issues
• Documentation: GoDoc
• Testing Guide: TESTING.md
• Contributing: CONTRIBUTING.md
• Source Code: GitHub Repository

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Security Disclosure

If you discover a security vulnerability, please email security@example.com (or create a private security advisory on GitHub). Do not disclose security issues publicly.

---

This package is part of the golib project.