d-subrahmanyam/cryptography

Cryptography

Password Hashing

bcrypt (recommended for most apps)

import bcrypt from 'bcrypt';

const SALT_ROUNDS = 12;

async function hashPassword(password: string): Promise<string> {
  return bcrypt.hash(password, SALT_ROUNDS);
}

async function verifyPassword(password: string, hash: string): Promise<boolean> {
  return bcrypt.compare(password, hash);
}

Argon2 (recommended for high-security)

import argon2 from 'argon2';

async function hashPassword(password: string): Promise<string> {
  return argon2.hash(password, {
    type: argon2.argon2id,
    memoryCost: 65536,  // 64 MB
    timeCost: 3,
    parallelism: 4,
  });
}

async function verifyPassword(password: string, hash: string): Promise<boolean> {
  return argon2.verify(hash, password);
}

Symmetric Encryption (AES-256-GCM)

import { createCipheriv, createDecipheriv, randomBytes } from 'crypto';

const ALGORITHM = 'aes-256-gcm';

function encrypt(plaintext: string, key: Buffer): string {
  const iv = randomBytes(12);
  const cipher = createCipheriv(ALGORITHM, key, iv);
  const encrypted = Buffer.concat([cipher.update(plaintext, 'utf8'), cipher.final()]);
  const authTag = cipher.getAuthTag();
  return Buffer.concat([iv, authTag, encrypted]).toString('base64');
}

function decrypt(ciphertext: string, key: Buffer): string {
  const buf = Buffer.from(ciphertext, 'base64');
  const iv = buf.subarray(0, 12);
  const authTag = buf.subarray(12, 28);
  const encrypted = buf.subarray(28);
  const decipher = createDecipheriv(ALGORITHM, key, iv);
  decipher.setAuthTag(authTag);
  return decipher.update(encrypted) + decipher.final('utf8');
}

// Key from environment (32 bytes for AES-256)
const key = Buffer.from(process.env.ENCRYPTION_KEY!, 'hex');

HMAC (Message Authentication)

import { createHmac, timingSafeEqual } from 'crypto';

function signPayload(payload: string, secret: string): string {
  return createHmac('sha256', secret).update(payload).digest('hex');
}

function verifySignature(payload: string, signature: string, secret: string): boolean {
  const expected = signPayload(payload, secret);
  return timingSafeEqual(Buffer.from(signature), Buffer.from(expected));
}

Secure Random Values

import { randomBytes, randomUUID } from 'crypto';

const token = randomBytes(32).toString('hex');  // 64-char hex token
const uuid = randomUUID();                       // UUID v4

Python

from passlib.hash import argon2
import os
from cryptography.fernet import Fernet

# Password hashing
hashed = argon2.hash("password")
is_valid = argon2.verify("password", hashed)

# Symmetric encryption
key = Fernet.generate_key()  # Store securely
f = Fernet(key)
encrypted = f.encrypt(b"sensitive data")
decrypted = f.decrypt(encrypted)

# Secure random
token = os.urandom(32).hex()

Anti-Patterns

| Anti-Pattern | Fix | |--------------|-----| | MD5/SHA for passwords | Use bcrypt or argon2 | | ECB mode encryption | Use GCM (authenticated encryption) | | Hardcoded keys | Use environment variables or KMS | | Math.random() for tokens | Use crypto.randomBytes() | | String comparison for signatures | Use timingSafeEqual() to prevent timing attacks | | Reusing IV/nonce | Generate fresh random IV for each encryption |

Production Checklist

• [ ] bcrypt (cost 12+) or argon2id for passwords
• [ ] AES-256-GCM for symmetric encryption
• [ ] Keys in environment variables or KMS
• [ ] crypto.randomBytes for all random tokens
• [ ] timingSafeEqual for signature verification
• [ ] Key rotation plan documented