OF-3257: Guard against timing attacks in ScramSha1SaslServer#3289
Merged
guusdk merged 7 commits intoigniterealtime:mainfrom May 5, 2026
Merged
OF-3257: Guard against timing attacks in ScramSha1SaslServer#3289guusdk merged 7 commits intoigniterealtime:mainfrom
guusdk merged 7 commits intoigniterealtime:mainfrom
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This was referenced Apr 23, 2026
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There is some overlap between the implementations in these two PRs:
Notably, the introduction of the same system property. Both PRs should introduce an exact duplicate. This, however, could trigger a merge conflict. |
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Pull request overview
This PR hardens Openfire’s SCRAM-SHA-1 SASL server implementation against timing-based side-channel attacks by avoiding early exits when credentials are missing, and by using constant-time comparisons for key material.
Changes:
- Introduces a new encrypted system property used to derive deterministic “fake” SCRAM keys for non-existing users.
- Updates SCRAM authentication to always compute equivalent HMAC work and to use
MessageDigest.isEqualfor constant-time key comparison. - Adds unit tests to validate determinism and variability of the generated fake keys, plus i18n strings for the new system property.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 9 comments.
| File | Description |
|---|---|
xmppserver/src/main/java/org/jivesoftware/openfire/sasl/ScramSha1SaslServer.java |
Adds server secret property + fake key generation and uses constant-time key comparison in SCRAM verification. |
xmppserver/src/test/java/org/jivesoftware/openfire/sasl/ScramSha1SaslServerFakeKeyTest.java |
Adds tests validating fake key behavior (determinism, variance by username/secret, expected length). |
i18n/src/main/resources/openfire_i18n.properties |
Adds system property description for the new SCRAM fake-key secret. |
i18n/src/main/resources/openfire_i18n_nl.properties |
Adds Dutch translation for the new system property description. |
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Fishbowler
requested changes
Apr 26, 2026
… fake keys When storedKey or serverKey are missing, generate deterministic fake values derived from a server-side secret and the username. This ensures that authentication follows the same execution path regardless of user existence, reducing susceptibility to timing attacks. Includes unit tests to verify determinism and key separation.
…AM-SHA-1(-PLUS) SASL server Previously, the comparison of the expected and received channel binding payloads in ScramSha1SaslServer used Arrays.equals, which is not guaranteed to operate in constant time. This could potentially leak information about the channel binding data through timing side-channels. This change replaces Arrays.equals with MessageDigest.isEqual, ensuring that the comparison is performed in constant time. This strengthens the implementation against timing attacks, aligns with secure coding best practices, and provides defense-in-depth for sensitive authentication operations.
…EXISTENT_USERS The previous method for one-time initialization of the SERVER_SECRET_NONEXISTENT_USERS property (which depended on a static initializer block) proved to be fragile. In this commit, initialization happens in a getter that should be used instead of directly accessing the property.
…setting the property after each test.
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I have rebased this on Main now that #3288 was merged there. |
Fishbowler
approved these changes
May 3, 2026
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This PR improves the resilience of the SCRAM-SHA-1 SASL implementation against timing-based side-channel attacks.
The changes focus on ensuring more consistent execution paths during authentication, particularly when handling non-existing users or missing credentials. Instead of short-circuiting, equivalent work is performed using substitute values to better align timing characteristics.
For detailed implementation specifics, see the individual commit messages.