SM2-PKE has Unchecked AffinePoint Decoding (unwrap) in decrypt()

QFinch assessment

A denial-of-service vulnerability exists in the SM2 PKE decryption path where an invalid elliptic-curve point (C1) is decoded and the resulting value is unwrapped without checking. Specifically, AffinePoint::fromencodedpoint(&encodedc1) may return a None/CtOption::None when the supplied coordinates are syntactically valid but do not lie on the SM2 curve. The calling code previously used .unwrap(), causing a panic when presented with such input.

Potential impact

- Denial of Service: an attacker who can submit ciphertext (or DER ciphertext) can crash the decrypting thread/process. - Low attacker effort: crafting random 32-byte X/Y values that are not on the curve is trivial. - Wide exposure: any service that accepts ciphertext and links this library is vulnerable.

Technical context

The library decodes the C1 field (an EC point) as an EncodedPoint and then converts it to an AffinePoint using AffinePoint::fromencodedpoint(&encodedc1). That conversion returns a CtOption<AffinePoint> (or an Option equivalent) which will indicate failure when the coordinates do not satisfy the curve equation. The code then called .unwrap() on that result, causing a panic when None was returned. Because EncodedPoint::frombytes() only validates format (length and SEC1 encoding) and not mathematical validity, an attacker can craft C1 = 0x04 || X || Y with X and Y of the right length that nonetheless do not satisfy the curve. Such inputs will pass the format check but trigger fromencodedpoint() failure and therefore panic on .unwrap().