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core/crypto: Misc cleanups and documentation improvements

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This commit is contained in:
Yawning Angel
2024-03-04 17:50:45 +09:00
parent b818ebc02f
commit fa8dd5a13b
5 changed files with 108 additions and 39 deletions
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core/crypto/x25519/x25519.odin
+19 -6
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@@ -1,9 +1,18 @@
/*
package x25519 implements the X25519 (aka curve25519) Elliptic-Curve
Diffie-Hellman key exchange protocol.
See:
- https://www.rfc-editor.org/rfc/rfc7748
*/
package x25519
import field "core:crypto/_fiat/field_curve25519"
import "core:mem"
// SCALAR_SIZE is the size of a X25519 scalar (private key) in bytes.
SCALAR_SIZE :: 32
// POINT_SIZE is the size of a X25519 point (public key/shared secret) in bytes.
POINT_SIZE :: 32
@(private)
@@ -14,11 +23,11 @@ _scalar_bit :: #force_inline proc "contextless" (s: ^[32]byte, i: int) -> u8 {
if i < 0 {
return 0
}
return (s[i>>3] >> uint(i&7)) & 1
return (s[i >> 3] >> uint(i & 7)) & 1
}
@(private)
_scalarmult :: proc (out, scalar, point: ^[32]byte) {
_scalarmult :: proc(out, scalar, point: ^[32]byte) {
// Montgomery pseduo-multiplication taken from Monocypher.
// computes the scalar product
@@ -26,7 +35,7 @@ _scalarmult :: proc (out, scalar, point: ^[32]byte) {
field.fe_from_bytes(&x1, point)
// computes the actual scalar product (the result is in x2 and z2)
x2, x3, z2, z3: field.Tight_Field_Element = ---, ---, ---, ---
x2, x3, z2, z3: field.Tight_Field_Element = ---, ---, ---, ---
t0, t1: field.Loose_Field_Element = ---, ---
// Montgomery ladder
@@ -38,7 +47,7 @@ _scalarmult :: proc (out, scalar, point: ^[32]byte) {
field.fe_one(&z3)
swap: int
for pos := 255-1; pos >= 0; pos = pos - 1 {
for pos := 255 - 1; pos >= 0; pos = pos - 1 {
// constant time conditional swap before ladder step
b := int(_scalar_bit(scalar, pos))
swap ~= b // xor trick avoids swapping at the end of the loop
@@ -94,7 +103,9 @@ _scalarmult :: proc (out, scalar, point: ^[32]byte) {
mem.zero_explicit(&t1, size_of(t1))
}
scalarmult :: proc (dst, scalar, point: []byte) {
// scalarmult "multiplies" the provided scalar and point, and writes the
// resulting point to dst.
scalarmult :: proc(dst, scalar, point: []byte) {
if len(scalar) != SCALAR_SIZE {
panic("crypto/x25519: invalid scalar size")
}
@@ -123,7 +134,9 @@ scalarmult :: proc (dst, scalar, point: []byte) {
mem.zero_explicit(&d, size_of(d))
}
scalarmult_basepoint :: proc (dst, scalar: []byte) {
// scalarmult_basepoint "multiplies" the provided scalar with the X25519
// base point and writes the resulting point to dst.
scalarmult_basepoint :: proc(dst, scalar: []byte) {
// TODO/perf: Switch to using a precomputed table.
scalarmult(dst, scalar, _BASE_POINT[:])
}