ecutil.go

Documentation: github.com/lestrrat-go/jwx/internal/ecutil

     1  // Package ecutil defines tools that help with elliptic curve related
     2  // computation
     3  package ecutil
     4  
     5  import (
     6  	"crypto/elliptic"
     7  	"math/big"
     8  	"sync"
     9  
    10  	"github.com/lestrrat-go/jwx/jwa"
    11  )
    12  
    13  // data for available curves. Some algorithms may be compiled in/out
    14  var curveToAlg = map[elliptic.Curve]jwa.EllipticCurveAlgorithm{}
    15  var algToCurve = map[jwa.EllipticCurveAlgorithm]elliptic.Curve{}
    16  var availableAlgs []jwa.EllipticCurveAlgorithm
    17  var availableCrvs []elliptic.Curve
    18  
    19  func RegisterCurve(crv elliptic.Curve, alg jwa.EllipticCurveAlgorithm) {
    20  	curveToAlg[crv] = alg
    21  	algToCurve[alg] = crv
    22  	availableAlgs = append(availableAlgs, alg)
    23  	availableCrvs = append(availableCrvs, crv)
    24  }
    25  
    26  func IsAvailable(alg jwa.EllipticCurveAlgorithm) bool {
    27  	_, ok := algToCurve[alg]
    28  	return ok
    29  }
    30  
    31  func AvailableAlgorithms() []jwa.EllipticCurveAlgorithm {
    32  	return availableAlgs
    33  }
    34  
    35  func AvailableCurves() []elliptic.Curve {
    36  	return availableCrvs
    37  }
    38  
    39  func AlgorithmForCurve(crv elliptic.Curve) (jwa.EllipticCurveAlgorithm, bool) {
    40  	v, ok := curveToAlg[crv]
    41  	return v, ok
    42  }
    43  
    44  func CurveForAlgorithm(alg jwa.EllipticCurveAlgorithm) (elliptic.Curve, bool) {
    45  	v, ok := algToCurve[alg]
    46  	return v, ok
    47  }
    48  
    49  const (
    50  	// size of buffer that needs to be allocated for EC521 curve
    51  	ec521BufferSize = 66 // (521 / 8) + 1
    52  )
    53  
    54  var ecpointBufferPool = sync.Pool{
    55  	New: func() interface{} {
    56  		// In most cases the curve bit size will be less than this length
    57  		// so allocate the maximum, and keep reusing
    58  		buf := make([]byte, 0, ec521BufferSize)
    59  		return &buf
    60  	},
    61  }
    62  
    63  func getCrvFixedBuffer(size int) []byte {
    64  	//nolint:forcetypeassert
    65  	buf := *(ecpointBufferPool.Get().(*[]byte))
    66  	if size > ec521BufferSize && cap(buf) < size {
    67  		buf = append(buf, make([]byte, size-cap(buf))...)
    68  	}
    69  	return buf[:size]
    70  }
    71  
    72  // ReleaseECPointBuffer releases the []byte buffer allocated.
    73  func ReleaseECPointBuffer(buf []byte) {
    74  	buf = buf[:cap(buf)]
    75  	buf[0] = 0x0
    76  	for i := 1; i < len(buf); i *= 2 {
    77  		copy(buf[i:], buf[:i])
    78  	}
    79  	buf = buf[:0]
    80  	ecpointBufferPool.Put(&buf)
    81  }
    82  
    83  // AllocECPointBuffer allocates a buffer for the given point in the given
    84  // curve. This buffer should be released using the ReleaseECPointBuffer
    85  // function.
    86  func AllocECPointBuffer(v *big.Int, crv elliptic.Curve) []byte {
    87  	// We need to create a buffer that fits the entire curve.
    88  	// If the curve size is 66, that fits in 9 bytes. If the curve
    89  	// size is 64, it fits in 8 bytes.
    90  	bits := crv.Params().BitSize
    91  
    92  	// For most common cases we know before hand what the byte length
    93  	// is going to be. optimize
    94  	var inBytes int
    95  	switch bits {
    96  	case 224, 256, 384: // TODO: use constant?
    97  		inBytes = bits / 8
    98  	case 521:
    99  		inBytes = ec521BufferSize
   100  	default:
   101  		inBytes = bits / 8
   102  		if (bits % 8) != 0 {
   103  			inBytes++
   104  		}
   105  	}
   106  
   107  	buf := getCrvFixedBuffer(inBytes)
   108  	v.FillBytes(buf)
   109  	return buf
   110  }
   111
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