Class SQIsignSigner

java.lang.Object
org.bouncycastle.pqc.crypto.sqisign.SQIsignSigner
All Implemented Interfaces:
MessageSigner
public class SQIsignSigner extends Object implements MessageSigner
SQIsign signer. Wired for all three NIST parameter sets (lvl1/lvl3/lvl5) via the polymorphic GfField-based dispatch in the EC/HD/theta layer.

Side-channel note: signing is not constant-time. SQIsign's arithmetic is implemented over BigInteger throughout — the GF(p) / GF(p²) base-field and elliptic-curve layer as well as the secret-key-dependent quaternion / ideal / lattice layer (commitment, challenge ideal, response sampling and the auxiliary isogeny). BigInteger operations are inherently variable-time, and the signing path additionally contains secret-dependent rejection loops and variable-iteration Euclidean / lattice-reduction (LLL, HNF, Cornacchia) steps. This matches the SQIsign reference implementation, whose KLPT / Clapotis layer is likewise variable-time. No constant-time guarantee can be made for signing or key generation; verification operates only on public values.

Deployment guidance: the long-term private key participates in the variable-time response / ideal-to-isogeny computation, so per-signature timing depends on secret material and can in principle accumulate toward the static key over many signatures. SQIsign signing therefore should not be exposed in settings where an adversary can measure the timing of signing operations performed under the same key — e.g. a remote timing oracle that signs attacker-influenced messages on demand, or a co-located / shared-host environment open to micro-architectural timing observation. This is an algorithmic property of SQIsign (the reference implementation shares it), not a limitation specific to this port, and there is no known practical constant-time formulation of the KLPT / lattice steps; treat it as a usage constraint until constant-time SQIsign techniques mature.

Signature malleability. A SQIsign signature is not a unique encoding of (key, message). SQIsignVerify.checkCanonicalBasisChangeMatrix bounds each entry of the basis-change matrix by 2^(response length + extra torsion - backtracking), but the verification arithmetic depends on the entry modulo a smaller power of two, so the top permitted bit of each of the four entries is not pinned down: at least sixteen distinct byte strings verify for any signature this signer produces. This is a property of the scheme rather than of the port - SQIsign is proved EUF-CMA but not strongly unforgeable, and the two-dimensional response encoding has further, deeper sources of non-uniqueness than the matrix (see eprint 2026/1305, which shows that canonicalising the matrix would not be sufficient). So unlike MAYO, SNOVA and QR-UOV, whose encodings this library does pin down, SQIsign signature bytes must not be used as a unique identifier for a signature - do not key a replay cache, a de-duplication table or an audit record on them.

  • Constructor Details

    • SQIsignSigner

      public SQIsignSigner()

  • Method Details

    • init

      public void init(boolean forSigning, CipherParameters param)
      Description copied from interface: MessageSigner
      initialise the signer for signature generation or signature verification.
      Specified by:
      init in interface MessageSigner
      Parameters:
      forSigning - true if we are generating a signature, false otherwise.
      param - key parameters for signature generation.

    • generateSignature

      public byte[] generateSignature(byte[] message)
      Description copied from interface: MessageSigner
      sign the passed in message (usually the output of a hash function).
      Specified by:
      generateSignature in interface MessageSigner
      Parameters:
      message - the message to be signed.
      Returns:
      the signature of the message

    • verifySignature

      public boolean verifySignature(byte[] message, byte[] signature)
      Description copied from interface: MessageSigner
      verify the message message against the signature value.
      Specified by:
      verifySignature in interface MessageSigner
      Parameters:
      message - the message that was supposed to have been signed.
      signature - the signature of the message