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// Package ecutil defines tools that help with elliptic curve related
// computation
package ecutil
import (
"crypto/elliptic"
"math/big"
"sync"
"github.com/lestrrat-go/jwx/v2/jwa"
)
// data for available curves. Some algorithms may be compiled in/out
var curveToAlg = map[elliptic.Curve]jwa.EllipticCurveAlgorithm{}
var algToCurve = map[jwa.EllipticCurveAlgorithm]elliptic.Curve{}
var availableAlgs []jwa.EllipticCurveAlgorithm
var availableCrvs []elliptic.Curve
func RegisterCurve(crv elliptic.Curve, alg jwa.EllipticCurveAlgorithm) {
curveToAlg[crv] = alg
algToCurve[alg] = crv
availableAlgs = append(availableAlgs, alg)
availableCrvs = append(availableCrvs, crv)
}
func IsAvailable(alg jwa.EllipticCurveAlgorithm) bool {
_, ok := algToCurve[alg]
return ok
}
func AvailableAlgorithms() []jwa.EllipticCurveAlgorithm {
return availableAlgs
}
func AvailableCurves() []elliptic.Curve {
return availableCrvs
}
func AlgorithmForCurve(crv elliptic.Curve) (jwa.EllipticCurveAlgorithm, bool) {
v, ok := curveToAlg[crv]
return v, ok
}
func CurveForAlgorithm(alg jwa.EllipticCurveAlgorithm) (elliptic.Curve, bool) {
v, ok := algToCurve[alg]
return v, ok
}
const (
// size of buffer that needs to be allocated for EC521 curve
ec521BufferSize = 66 // (521 / 8) + 1
)
var ecpointBufferPool = sync.Pool{
New: func() interface{} {
// In most cases the curve bit size will be less than this length
// so allocate the maximum, and keep reusing
buf := make([]byte, 0, ec521BufferSize)
return &buf
},
}
func getCrvFixedBuffer(size int) []byte {
//nolint:forcetypeassert
buf := *(ecpointBufferPool.Get().(*[]byte))
if size > ec521BufferSize && cap(buf) < size {
buf = append(buf, make([]byte, size-cap(buf))...)
}
return buf[:size]
}
// ReleaseECPointBuffer releases the []byte buffer allocated.
func ReleaseECPointBuffer(buf []byte) {
buf = buf[:cap(buf)]
buf[0] = 0x0
for i := 1; i < len(buf); i *= 2 {
copy(buf[i:], buf[:i])
}
buf = buf[:0]
ecpointBufferPool.Put(&buf)
}
func CalculateKeySize(crv elliptic.Curve) int {
// We need to create a buffer that fits the entire curve.
// If the curve size is 66, that fits in 9 bytes. If the curve
// size is 64, it fits in 8 bytes.
bits := crv.Params().BitSize
// For most common cases we know before hand what the byte length
// is going to be. optimize
var inBytes int
switch bits {
case 224, 256, 384: // TODO: use constant?
inBytes = bits / 8
case 521:
inBytes = ec521BufferSize
default:
inBytes = bits / 8
if (bits % 8) != 0 {
inBytes++
}
}
return inBytes
}
// AllocECPointBuffer allocates a buffer for the given point in the given
// curve. This buffer should be released using the ReleaseECPointBuffer
// function.
func AllocECPointBuffer(v *big.Int, crv elliptic.Curve) []byte {
buf := getCrvFixedBuffer(CalculateKeySize(crv))
v.FillBytes(buf)
return buf
}
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