Add curve25519 impl

src/crypto/curve25519.nim

@@ -0,0 +1,61 @@
+# Reference: https://github.com/vacp2p/mix/blob/main/src/curve25519.nim
+
+
+import results
+import bearssl/rand
+import libp2p/crypto/curve25519
+
+const FieldElementSize* = Curve25519KeySize
+
+type FieldElement* = Curve25519Key
+
+# Convert bytes to FieldElement
+proc bytesToFieldElement*(bytes: openArray[byte]): Result[FieldElement, string] =
+  if bytes.len != FieldElementSize:
+    return err("Field element size must be 32 bytes")
+  ok(intoCurve25519Key(bytes))
+
+# Convert FieldElement to bytes
+proc fieldElementToBytes*(fe: FieldElement): seq[byte] =
+  fe.getBytes()
+
+# Generate a random FieldElement
+proc generateRandomFieldElement*(): Result[FieldElement, string] =
+  let rng = HmacDrbgContext.new()
+  if rng.isNil:
+    return err("Failed to creat HmacDrbgContext with system randomness")
+  ok(Curve25519Key.random(rng[]))
+
+# Generate a key pair (private key and public key are both FieldElements)
+proc generateKeyPair*(): Result[tuple[privateKey, publicKey: FieldElement], string] =
+  let privateKeyRes = generateRandomFieldElement()
+  if privateKeyRes.isErr:
+    return err(privateKeyRes.error)
+  let privateKey = privateKeyRes.get()
+
+  let publicKey = public(privateKey)
+  ok((privateKey, publicKey))
+
+# Multiply a given Curve25519 point with a set of scalars
+proc multiplyPointWithScalars*(
+    point: FieldElement, scalars: openArray[FieldElement]
+): FieldElement =
+  var res = point
+  for scalar in scalars:
+    Curve25519.mul(res, scalar)
+  res
+
+# Multiply the Curve25519 base point with a set of scalars
+proc multiplyBasePointWithScalars*(
+    scalars: openArray[FieldElement]
+): Result[FieldElement, string] =
+  if scalars.len <= 0:
+    return err("Atleast one scalar must be provided")
+  var res: FieldElement = public(scalars[0]) # Use the predefined base point
+  for i in 1 ..< scalars.len:
+    Curve25519.mul(res, scalars[i]) # Multiply with each scalar
+  ok(res)
+
+# Compare two FieldElements
+proc compareFieldElements*(a, b: FieldElement): bool =
+  a == b