31 lines
702 B
Go
31 lines
702 B
Go
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package crypto
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import "fmt"
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// ConstantTimeByteCompare is a constant-time byte comparison of x and y. This function performs an absolute comparison
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// if the two byte slices assuming they represent a big-endian number.
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//
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// error if len(x) != len(y)
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// -1 if x < y
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// 0 if x == y
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// +1 if x > y
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func ConstantTimeByteCompare(x, y []byte) (int, error) {
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if len(x) != len(y) {
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return 0, fmt.Errorf("slice lengths do not match")
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}
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xLarger, yLarger := 0, 0
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for i := 0; i < len(x); i++ {
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xByte, yByte := int(x[i]), int(y[i])
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x := ((yByte - xByte) >> 8) & 1
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y := ((xByte - yByte) >> 8) & 1
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xLarger |= x &^ yLarger
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yLarger |= y &^ xLarger
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}
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return xLarger - yLarger, nil
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}
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