Pre-image resistance

As explained in Hacking Cryptography

The security property that makes it computationally infeasible to find an input corresponding to a specified hash output.

Pre-image resistance is the requirement that, given a digest Y = H(A), an attacker cannot feasibly recover the original input A. It is also called first pre-image resistance and expresses the one-way behavior of a hash function. section 6.2 section 6.5

A fixed-size digest compresses inputs of unlimited size, so collisions must exist in theory; pre-image resistance instead concerns the difficulty of reversing one chosen digest to its input. section 6.2 section 6.5

Keep these distinctions clear:

• Pre-image resistance asks for A when Y = H(A) is known. section 6.2
• Second pre-image resistance asks for a different B matching the digest of a known A. section 6.2
• Collision resistance asks for any pair of inputs with the same digest, without fixing the digest first. section 6.2
• Dictionary attacks weaken password secrecy by precomputing digests for likely valid passwords and performing reverse lookups. section 6.0 section 6.5

Password hash

A stored password digest should not reveal the exact password used to produce it. An attacker who obtains Y should face an infeasible search for A, although likely-password dictionaries can provide a practical attack path. section 6.2 section 6.5

Figure 6.4 Security properties of hash functions

Compare pre-image resistance with second pre-image and collision resistance in the security-property diagram. section 6.2

How Hacking Cryptography covers it

How deep it goes

Defines the attacker’s target and distinguishes it from related properties, but does not develop a concrete inversion algorithm.

Examples

Uses password digests, reverse-looked-up password dictionaries, and fixed-size hash outputs as concrete illustrations.

What it assumes

Assumes basic familiarity with hash functions and digest notation while explaining the security terminology from its definitions.

What you can do after

Evaluate hash security claims by distinguishing reversal of a chosen digest from second-preimage and collision attacks.

How it connects

Connects pre-image resistance to hash functions, one-way functions, second pre-image resistance, collision resistance, and dictionary attacks.

liveBookmanning.com

Read Hacking Cryptography on liveBook Get the book at manning.com

Also explained in

• 

  liveBookmanning.com
  Real-World CryptographyPre-image resistance is the property that, given a hash output, it is computationally infeasible to find an input that hashes to that output.

Compare how 2 books explain pre-image resistance →

Related concepts

• hash-based signature schemeused by · A hash-based signature scheme is a digital signature scheme whose security is based on cryptographic hash-function properties rather than algebraic number-theoretic assumptions.
• hash functionproduced by · A hash function deterministically maps input data to a value in a bounded output range, commonly for indexing, lookup, comparison, or integrity checking.
• security propertykind of · A security property is a security-relevant characteristic that a cryptographic primitive or protocol is intended to provide.
• second pre-image resistancecontrasts with · Second pre-image resistance is the property that, given an input and its hash, finding a different input with the same hash is computationally infeasible.

This explainer was generated by Manning's knowledge graph from the text of Hacking Cryptography. The section links point to the parts of the book it draws on.