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Cryptographic Tools

Crypto tools

What is HMAC?

HMAC (Hash-based Message Authentication Code) is a cryptographic technique that combines a hash function with a secret key to create a message authentication code. It provides both data integrity and authenticity verification, ensuring that a message hasn't been tampered with and comes from a trusted source.

  • Data Integrity: Detects any changes to the original message
  • Authentication: Verifies the message comes from someone with the secret key
  • Non-repudiation: Proves the sender cannot deny sending the message
  • Key-dependent: Same message with different keys produces different HMACs

HMAC Generator

Crypto
The data you want to authenticate and verify integrity for.
The secret key used to generate the HMAC. Keep this secure!
Choose the hash function to use with HMAC.
How HMAC Works
  1. Key Padding: Secret key is padded to match hash block size
  2. Inner Hash: Key ⊕ inner_pad + message → hash
  3. Outer Hash: Key ⊕ outer_pad + inner_hash → final HMAC
  4. Result: Fixed-length authentication code
Common Use Cases
  • API Authentication: Verify API requests
  • Digital Signatures: Sign documents and messages
  • Session Tokens: Secure session management
  • Data Integrity: Verify file downloads
  • Password Storage: Hash passwords with salts
  • Blockchain: Verify transaction integrity
Algorithm Comparison
Algorithm Output Size Security
SHA-256 256 bits Strong
SHA-512 512 bits Strongest
SHA-1 160 bits Weak
MD5 128 bits Broken
Example

Message: "Hello, World!"

Key: "mySecretKey123"

Algorithm: SHA-256

HMAC: a4d7c0...

Best Practices
  • Use SHA-256 or SHA-512 for security
  • Keep your secret key confidential
  • Use random, long keys (32+ characters)
  • Never reuse keys across different purposes
  • Store keys securely (not in code)
  • Rotate keys periodically
Resources