Balloon hashing

Balloon hashing is a key derivation function presenting proven memory-hard password-hashing and modern design. It was created by Dan Boneh, Henry Corrigan-Gibbs (both at Stanford University) and Stuart Schechter (Microsoft Research) in 2016.^[1][2] It is a recommended function in NIST password guidelines.^[3]

The authors claim that Balloon:

• has proven memory-hardness properties,
• is built from standard primitives: it can use any standards non-space-hard cryptographic hash function as a sub-algorithm (e.g., SHA-3, SHA-512),
• is resistant to side-channel attacks: the memory access pattern is independent of the data to be hashed,
• is easy to implement and matches the performance of similar algorithms.

Balloon is compared by its authors with Argon2, a similarly performing algorithm.^[1]

Algorithm

There are three steps in the algorithm:^[1]

1. Expansion, where an initial buffer is filled with a pseudorandom byte sequence derived from the password and salt repeatedly hashed.
2. Mixing, where the bytes in the buffer are mixed time_cost number of times.
3. Output, where a portion of the buffer is taken as the hashing result.

References

1. Boneh, Dan; Corrigan-Gibbs, Henry; Schechter, Stuart (2016-01-11). "Balloon Hashing: A Memory-Hard Function Providing Provable Protection Against Sequential Attacks". ePrint. 2016 (27). Retrieved 2019-09-03.
2. "Balloon Hashing". Stanford Applied Crypto Group. Stanford University. Retrieved 2019-09-03.
3. NIST SP800-63B Section 5.1.1.2

External links

• Research prototype code on Github
• Python implementation
• Rust implementation
• Alwen; Blocki (2016). "Efficiently Computing Data-Independent Memory-Hard Functions". ePrint. 2016 (115).
• Alwen; Blocki (2016). "Towards Practical Attacks on Argon2i and Balloon Hashing". ePrint. 2016 (759).