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Password-authenticated key exchange (PAK) protocol
StatusIn force
Year started2007
Latest version(09/07)
September 2007
CommitteeStudy Group 17

ITU-T Recommendation X.1035 specifies a password-authenticated key agreement protocol that ensures mutual authentication of two parties by using a Diffie–Hellman key exchange to establish a symmetric cryptographic key. The use of Diffie-Hellman exchange ensures perfect forward secrecy—a property of a key establishment protocol that guarantees that compromise of a session key or long-term private key after a given session does not cause the compromise of any earlier session.

In X.1035, the exchange is protected from the man-in-the-middle attack. The authentication relies on a pre-shared secret (e.g., password), which is protected (i.e., remains unrevealed) to an eavesdropper preventing an off-line dictionary attack.[1]

The protocol can be used in a wide variety of applications including those with pre-shared secrets based on possibly weak passwords.

X.1035 was approved on 13 February 2007 by ITU-T Study Group 17.[2]


G.hn, an ITU-T standard that specifies high-speed (up to 1 Gbit/s) local area networking over existing home wires (power lines, phone lines and coaxial cables), uses X.1035 for authentication and key exchange.


  1. ^ Andreasson, Kim J. (2012-05-17). Cybersecurity: Public Sector Threats and Responses. CRC Press. p. 151. ISBN 9781466551237.
  2. ^ "X.1035 : Password-authenticated key exchange (PAK) protocol". www.itu.int. Archived from the original on 2019-11-14. Retrieved 2019-11-14.