110 lines
2.7 KiB
Go
110 lines
2.7 KiB
Go
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// Package ecutil defines tools that help with elliptic curve related
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// computation
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package ecutil
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import (
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"crypto/elliptic"
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"math/big"
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"sync"
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"github.com/lestrrat-go/jwx/jwa"
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)
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// data for available curves. Some algorithms may be compiled in/out
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var curveToAlg = map[elliptic.Curve]jwa.EllipticCurveAlgorithm{}
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var algToCurve = map[jwa.EllipticCurveAlgorithm]elliptic.Curve{}
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var availableAlgs []jwa.EllipticCurveAlgorithm
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var availableCrvs []elliptic.Curve
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func RegisterCurve(crv elliptic.Curve, alg jwa.EllipticCurveAlgorithm) {
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curveToAlg[crv] = alg
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algToCurve[alg] = crv
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availableAlgs = append(availableAlgs, alg)
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availableCrvs = append(availableCrvs, crv)
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}
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func IsAvailable(alg jwa.EllipticCurveAlgorithm) bool {
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_, ok := algToCurve[alg]
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return ok
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}
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func AvailableAlgorithms() []jwa.EllipticCurveAlgorithm {
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return availableAlgs
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}
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func AvailableCurves() []elliptic.Curve {
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return availableCrvs
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}
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func AlgorithmForCurve(crv elliptic.Curve) (jwa.EllipticCurveAlgorithm, bool) {
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v, ok := curveToAlg[crv]
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return v, ok
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}
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func CurveForAlgorithm(alg jwa.EllipticCurveAlgorithm) (elliptic.Curve, bool) {
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v, ok := algToCurve[alg]
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return v, ok
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}
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const (
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// size of buffer that needs to be allocated for EC521 curve
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ec521BufferSize = 66 // (521 / 8) + 1
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)
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var ecpointBufferPool = sync.Pool{
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New: func() interface{} {
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// In most cases the curve bit size will be less than this length
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// so allocate the maximum, and keep reusing
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buf := make([]byte, 0, ec521BufferSize)
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return &buf
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},
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}
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func getCrvFixedBuffer(size int) []byte {
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buf := *(ecpointBufferPool.Get().(*[]byte))
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if size > ec521BufferSize && cap(buf) < size {
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buf = append(buf, make([]byte, size-cap(buf))...)
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}
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return buf[:size]
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}
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// ReleaseECPointBuffer releases the []byte buffer allocated.
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func ReleaseECPointBuffer(buf []byte) {
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buf = buf[:cap(buf)]
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buf[0] = 0x0
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for i := 1; i < len(buf); i *= 2 {
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copy(buf[i:], buf[:i])
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}
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buf = buf[:0]
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ecpointBufferPool.Put(&buf)
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}
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// AllocECPointBuffer allocates a buffer for the given point in the given
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// curve. This buffer should be released using the ReleaseECPointBuffer
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// function.
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func AllocECPointBuffer(v *big.Int, crv elliptic.Curve) []byte {
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// We need to create a buffer that fits the entire curve.
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// If the curve size is 66, that fits in 9 bytes. If the curve
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// size is 64, it fits in 8 bytes.
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bits := crv.Params().BitSize
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// For most common cases we know before hand what the byte length
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// is going to be. optimize
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var inBytes int
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switch bits {
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case 224, 256, 384: // TODO: use constant?
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inBytes = bits / 8
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case 521:
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inBytes = ec521BufferSize
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default:
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inBytes = bits / 8
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if (bits % 8) != 0 {
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inBytes++
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}
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}
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buf := getCrvFixedBuffer(inBytes)
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v.FillBytes(buf)
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return buf
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}
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