A cryptographer has developed a new proprietary hash function for a company and solicited employees to test the function before recommending its implementation. An employee takes the plaintext version of a document and hashes it, then changes the original plaintext document slightly and hashes it, and continues repeating this process until two identical hash values are produced from two different documents. Which of the following BEST describes this cryptographic attack?

• Brute force
• Known plaintext
• Replay
• Collision