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