BLAKE2b: 256 vs 512 – Which is Best?

TL;DR

Choose BLAKE2b-512 for stronger security, especially if you have the resources. If speed and smaller output size are critical and you’re confident in your threat model, BLAKE2b-256 is acceptable. For most applications, BLAKE2b-512 is the recommended choice.

Understanding BLAKE2b

BLAKE2b is a fast cryptographic hash function. It’s often used for data integrity checks, password hashing, and digital signatures. The ‘b’ indicates it’s optimised for 64-bit platforms. The key difference between BLAKE2b-256 and BLAKE2b-512 is the output size (hash length).

Step-by-step Guide: Choosing Between BLAKE2b-256 and BLAKE2b-512

1. Hash Lengths Explained
   • BLAKE2b-256: Produces a 256-bit (32-byte) hash.
   • BLAKE2b-512: Produces a 512-bit (64-byte) hash.
2. Security Considerations
   • A longer hash length generally provides better security against collision attacks (finding two different inputs that produce the same hash).
   • BLAKE2b-512 offers a larger theoretical attack surface, making it more resistant to future cryptographic advancements and potential weaknesses.
   • While BLAKE2b-256 is still considered secure for many applications, BLAKE2b-512 provides an extra margin of safety.
3. Performance Impact
   • BLAKE2b-512 will be slightly slower than BLAKE2b-256 due to the increased computational complexity. However, the difference is often negligible on modern hardware.
   • If you’re processing very large volumes of data, performance testing is recommended to determine if the speed difference is significant for your use case.
4. Storage Requirements
   • BLAKE2b-512 requires more storage space than BLAKE2b-256 (64 bytes vs 32 bytes). This might be a factor if you’re storing hashes in large databases or have limited storage capacity.
5. Example Usage with OpenSSL

   Here’s how to generate hashes using OpenSSL:

   • BLAKE2b-256:

     openssl dgst -blake2b256 input.txt

   • BLAKE2b-512:

     openssl dgst -blake2b512 input.txt

6. Example Usage with Python (hashlib)

   Here’s how to generate hashes using Python’s hashlib library:

   • BLAKE2b-256:

     import hashlib
     with open('input.txt', 'rb') as f:
       data = f.read()
     hash_object = hashlib.blake2b(data, digest_size=32)
     hex_dig = hash_object.hexdigest()
     print(hex_dig)

   • BLAKE2b-512:

     import hashlib
     with open('input.txt', 'rb') as f:
       data = f.read()
     hash_object = hashlib.blake2b(data, digest_size=64)
     hex_dig = hash_object.hexdigest()
     print(hex_dig)

7. Consider Your Threat Model
   • If you’re dealing with highly sensitive data or are concerned about advanced attackers, BLAKE2b-512 is the safer option.
   • For less critical applications where speed and storage are paramount, BLAKE2b-256 may be sufficient.

Summary

BLAKE2b-512 is generally the preferred choice due to its stronger security properties. However, BLAKE2b-256 remains a viable option if performance and storage are critical constraints and your threat model allows it.