From: Chris Duncan <chris@zoso.dev>
Date: Fri, 5 Dec 2025 23:01:49 +0000 (-0800)
Subject: Consolidate bigint cast to bytes since we already validate it before we use it.
X-Git-Url: https://git.codecow.com/?a=commitdiff_plain;h=2f1e37ca92d0fdb7a9064be120a36da6a24e3100;p=libnemo.git

Consolidate bigint cast to bytes since we already validate it before we use it.
---

diff --git a/src/lib/crypto/secp256k1.ts b/src/lib/crypto/secp256k1.ts
index 2daef48..73ea0ea 100644
--- a/src/lib/crypto/secp256k1.ts
+++ b/src/lib/crypto/secp256k1.ts
@@ -231,27 +231,13 @@ export class Secp256k1 {
 		return int
 	}
 
-	/** Number to 32b. Must be 0 <= num < 2²⁵⁶. validate, pad, to bytes. */
-	static bigintTo32Bytes (num: bigint): Bytes {
-		this.bigintInRange(num, 0n, 2n ** 256n) // secp256k1 is weierstrass curve. Equation is x³ + ax + b.
-		let len = this.L, bytes = new Uint8Array(len)
-		for (let i = len - 1; i >= 0; i--) {
-			bytes[i] = Number(num & 0xffn)
-			num >>= 8n
-		}
-		return bytes
-	}
-
 	/** Checks if the point is valid and on-curve. */
-	static isValidPoint (p?: Point): Point {
-		if (p) {
-			const { x, y } = this.Affine(p) // convert to 2d xy affine point.
-			this.bigintInRange(x, 1n, this.P) // must be in range 1 <= x,y < P
-			this.bigintInRange(y, 1n, this.P)
-			// y² == x³ + ax + b, equation sides must be equal
-			return this.M(y * y) === this.koblitz(x) ? p : this.err('bad point: not on curve')
-		}
-		this.err('bad point: undefined')
+	static isValidPoint (p: Point): Point {
+		const { x, y } = this.Affine(p) // convert to 2d xy affine point.
+		this.bigintInRange(x, 1n, this.P) // must be in range 1 <= x,y < P
+		this.bigintInRange(y, 1n, this.P)
+		// y² == x³ + ax + b, equation sides must be equal
+		return this.M(y * y) === this.koblitz(x) ? p : this.err('bad point: not on curve')
 	}
 
 	/** Normalize private key to scalar (bigint). Verifies scalar is in range 1<s<N */
@@ -277,23 +263,18 @@ export class Secp256k1 {
 	/** Converts point to 33-byte Uint8Array and checks validity. */
 	static isValidPublicKey (pk: Bytes): boolean {
 		if (pk.length !== this.C) return false
+		const prefix = pk[0]
+		if (prefix !== 0x02 && prefix !== 0x03) return false
+		const evenH = prefix === 0x02
 		try {
 			this.abytes(pk)
-			let p: Point | undefined = undefined
-			const length = pk.length
-			const head = pk[0]
-			const tail = pk.subarray(1)
-			const x = this.bytesToBigint(tail.subarray(0, this.L))
-			// No actual validation is done here until calling isValidPoint()
-			if (length === this.C && (head === 0x02 || head === 0x03)) {
-				// Equation is y² == x³ + ax + b. We calculate y from x.
-				// y = √y²; there are two solutions: y, -y. Determine proper solution based on prefix
-				let y = this.lift_x(x)
-				const evenY = this.isEven(y)
-				const evenH = this.isEven(BigInt(head))
-				if (evenH !== evenY) y = this.M(-y)
-				p = this.Point(x, y, 1n)
-			}
+			const x = this.bytesToBigint(pk.subarray(1))
+			// Equation is y² == x³ + ax + b. We calculate y from x.
+			// y = √y²; there are two solutions: y, -y. Determine proper solution based on SEC1 prefix
+			let y = this.lift_x(x)
+			const evenY = this.isEven(y)
+			if (evenH !== evenY) y = this.M(-y)
+			const p = this.Point(x, y, 1n)
 			// Validate point
 			return !!this.isValidPoint(p)
 		} catch (error) {