Fix Poseidon V1 suffix-zero collision

[jayz22]

What

Fix Poseidon V1 suffix-zero collision vulnerability, where hash([x]) == hash([x, 0]) when using a sponge with T > inputs.len() + 1, by enforcing inputs.len() == RATE (full-rate) for Poseidon V1.

Matches circom's behavior where nInputs always determines T = nInputs + 1, so the rate is always fully used

Poseidon2 is unaffected (already uses IV = input_len << 64 for domain separation)

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	soroban-sdk@​25.0.2 ⏵ 25.3.0

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[Copilot]

Pull request overview

This PR mitigates a Poseidon V1 suffix-zero collision (hash([x]) == hash([x, 0]) under partial-rate usage) by enforcing full-rate input absorption (inputs.len() == RATE) to align with circom’s T = nInputs + 1 behavior.

Changes:

• Enforce inputs.len() == RATE for Poseidon V1 (reject partial-rate and empty inputs via the same invariant).
• Improve Poseidon2’s rate-exceeded panic message and update tests accordingly.
• Update public docs/README to reflect the Poseidon V1 full-rate requirement, and bump soroban-sdk to 25.3.0.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/poseidon/sponge.rs	Enforces full-rate (== RATE) absorption for Poseidon V1 and updates panic/docs accordingly.
src/tests/poseidon.rs	Replaces partial-rate behavior tests with partial-rate rejection tests; updates panic expectations.
src/lib.rs	Updates Poseidon V1 API docs to require T == inputs.len() + 1.
README.md	Documents Poseidon V1 full-rate constraint vs Poseidon2’s <= rate constraint.
src/poseidon2/sponge.rs	Adds a clearer assert message when inputs exceed the Poseidon2 rate.
src/tests/poseidon2.rs	Updates the expected panic message for the Poseidon2 exceed-rate test.
Cargo.toml	Bumps workspace soroban-sdk dependency to 25.3.0.
Cargo.lock	Lockfile updates corresponding to the soroban-sdk bump.

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