ShortSignatures in BLS

[secure12]

I have been using @noble/curves v1.2.0 to extend the BLS class to BLS12-377. It works quite well. But today, when I wanted to update the package to v1.4.0, there are type errors because ShortSignatures were added and are required in BLS. I don't need signatures in my application, it seems weird that they are compulsory in the class.

Also, the missing functions are just serialisation of signatures (to/from hex/bytes). Why does the short signature implementation need to re-implement the same functionalities in the EC groups? Aren't the signatures group elements themselves?
E.g.

noble-curves/src/bls12-381.ts

Lines 1201 to 1216 in e14e37a

	fromHex(hex: Hex): ProjPointType<Fp> {
	const { infinity, sort, value } = parseMask(ensureBytes('signatureHex', hex, 48));
	const P = Fp.ORDER;
	const compressedValue = bytesToNumberBE(value);
	// Zero
	if (infinity) return bls12_381.G1.ProjectivePoint.ZERO;
	const x = Fp.create(compressedValue & Fp.MASK);
	const right = Fp.add(Fp.pow(x, _3n), Fp.create(bls12_381.params.G1b)); // y² = x³ + b
	let y = Fp.sqrt(right);
	if (!y) throw new Error('Invalid compressed G1 point');
	const aflag = BigInt(sort);
	if ((y * _2n) / P !== aflag) y = Fp.neg(y);
	const point = bls12_381.G1.ProjectivePoint.fromAffine({ x, y });
	point.assertValidity();
	return point;
	},

and

noble-curves/src/bls12-381.ts

Lines 1152 to 1181 in e14e37a

	fromBytes: (bytes: Uint8Array): AffinePoint<Fp> => {
	const { compressed, infinity, sort, value } = parseMask(bytes);
	if (value.length === 48 && compressed) {
	// TODO: Fp.bytes
	const P = Fp.ORDER;
	const compressedValue = bytesToNumberBE(value);
	// Zero
	const x = Fp.create(compressedValue & Fp.MASK);
	if (infinity) {
	if (x !== _0n) throw new Error('G1: non-empty compressed point at infinity');
	return { x: _0n, y: _0n };
	}
	const right = Fp.add(Fp.pow(x, _3n), Fp.create(bls12_381.params.G1b)); // y² = x³ + b
	let y = Fp.sqrt(right);
	if (!y) throw new Error('Invalid compressed G1 point');
	if ((y * _2n) / P !== BigInt(sort)) y = Fp.neg(y);
	return { x: Fp.create(x), y: Fp.create(y) };
	} else if (value.length === 96 && !compressed) {
	// Check if the infinity flag is set
	const x = bytesToNumberBE(value.subarray(0, Fp.BYTES));
	const y = bytesToNumberBE(value.subarray(Fp.BYTES));
	if (infinity) {
	if (x !== _0n || y !== _0n) throw new Error('G1: non-empty point at infinity');
	return bls12_381.G1.ProjectivePoint.ZERO.toAffine();
	}
	return { x: Fp.create(x), y: Fp.create(y) };
	} else {
	throw new Error('Invalid point G1, expected 48/96 bytes');
	}
	},

are very similar. Will there be an issue if ShortSignature.fromHex just use G1.fromBytes (subject to refactoring)?

[paulmillr]

I don't need signatures in my application, it seems weird that they are compulsory in the class.

Then you can safely make ShortSignature.fromHex empty.

Also, consider contributing bls377 to the repo!