mirror of
https://github.com/henrydcase/nobs.git
synced 2024-11-25 00:21:29 +00:00
47 lines
1.2 KiB
Go
47 lines
1.2 KiB
Go
package common
|
|
|
|
// Constant time select.
|
|
// if pick == 1 (out = in1)
|
|
// if pick == 0 (out = in2)
|
|
// else out is undefined.
|
|
func Cpick(pick int, out, in1, in2 []byte) {
|
|
var which = byte((int8(pick << 7)) >> 7)
|
|
for i := range out {
|
|
out[i] = (in1[i] & which) | (in2[i] & ^which)
|
|
}
|
|
}
|
|
|
|
// Read 2*bytelen(p) bytes into the given ExtensionFieldElement.
|
|
//
|
|
// It is an error to call this function if the input byte slice is less than 2*bytelen(p) bytes long.
|
|
func BytesToFp2(fp2 *Fp2, input []byte, bytelen int) {
|
|
if len(input) < 2*bytelen {
|
|
panic("input byte slice too short")
|
|
}
|
|
|
|
for i := 0; i < bytelen; i++ {
|
|
j := i / 8
|
|
k := uint64(i % 8)
|
|
fp2.A[j] |= uint64(input[i]) << (8 * k)
|
|
fp2.B[j] |= uint64(input[i+bytelen]) << (8 * k)
|
|
}
|
|
}
|
|
|
|
// Convert the input to wire format.
|
|
//
|
|
// The output byte slice must be at least 2*bytelen(p) bytes long.
|
|
func Fp2ToBytes(output []byte, fp2 *Fp2, bytelen int) {
|
|
if len(output) < 2*bytelen {
|
|
panic("output byte slice too short")
|
|
}
|
|
|
|
// convert to bytes in little endian form
|
|
for i := 0; i < bytelen; i++ {
|
|
// set i = j*8 + k
|
|
tmp := i / 8
|
|
k := uint64(i % 8)
|
|
output[i] = byte(fp2.A[tmp] >> (8 * k))
|
|
output[i+bytelen] = byte(fp2.B[tmp] >> (8 * k))
|
|
}
|
|
}
|