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Digest authentication

Digest authentication

(also digest access authentication)

Digest authentication definition

Digest authentication is a method used to verify the identity of a user or device requesting access to a secure system, such as a website or network. Digest authentication uses a combination of a username, password, and a unique message digest (a type of encrypted code).

See also: replay attack

How digest authentication works

  1. The user requests to access a protected system (like their bank’s website or a social media profile).
  2. The system responds with a unique challenge — a random string of characters.
  3. The user enters their username and password when prompted.
  4. The user’s web browser combines the password with the challenge and applies a special algorithm (hashing) to create a message digest.
  5. The user sends the message digest to the system as part of their authentication request.
  6. The system receives the message digest and performs the same calculation using the user’s password and the challenge it sent earlier.
  7. If the message digest calculated by the system matches the one sent by the user, it means the user provided the correct password and is granted access.

Benefits of digest authentication

  • Password protection. Digest authentication ensures that passwords aren’t transmitted over the network in plain text. Only the message digest (or encrypted code) is exchanged, protecting passwords from being intercepted.
  • Reduced vulnerability to replay attacks. Digest authentication includes a nonce (number used once) in the challenge, making each authentication request unique. This prevents replay attacks (where an attacker intercepts and reuses a previously captured authentication request).
  • Protection against eavesdropping. By using hashing algorithms to generate message digests, digest authentication protects against eavesdropping attacks. Even if an attacker intercepts the authentication request, they cannot attain the original password from the message digest.

Further reading

Ultimate digital security