ecdsa_s390x.go

Documentation: crypto/ecdsa

     1  // Copyright 2020 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package ecdsa
     6  
     7  import (
     8  	"crypto/cipher"
     9  	"crypto/elliptic"
    10  	"internal/cpu"
    11  	"math/big"
    12  )
    13  
    14  // kdsa invokes the "compute digital signature authentication"
    15  // instruction with the given function code and 4096 byte
    16  // parameter block.
    17  //
    18  // The return value corresponds to the condition code set by the
    19  // instruction. Interrupted invocations are handled by the
    20  // function.
    21  //go:noescape
    22  func kdsa(fc uint64, params *[4096]byte) (errn uint64)
    23  
    24  // testingDisableKDSA forces the generic fallback path. It must only be set in tests.
    25  var testingDisableKDSA bool
    26  
    27  // canUseKDSA checks if KDSA instruction is available, and if it is, it checks
    28  // the name of the curve to see if it matches the curves supported(P-256, P-384, P-521).
    29  // Then, based on the curve name, a function code and a block size will be assigned.
    30  // If KDSA instruction is not available or if the curve is not supported, canUseKDSA
    31  // will set ok to false.
    32  func canUseKDSA(c elliptic.Curve) (functionCode uint64, blockSize int, ok bool) {
    33  	if testingDisableKDSA {
    34  		return 0, 0, false
    35  	}
    36  	if !cpu.S390X.HasECDSA {
    37  		return 0, 0, false
    38  	}
    39  	switch c.Params().Name {
    40  	case "P-256":
    41  		return 1, 32, true
    42  	case "P-384":
    43  		return 2, 48, true
    44  	case "P-521":
    45  		return 3, 80, true
    46  	}
    47  	return 0, 0, false // A mismatch
    48  }
    49  
    50  func hashToBytes(dst, hash []byte, c elliptic.Curve) {
    51  	l := len(dst)
    52  	if n := c.Params().N.BitLen(); n == l*8 {
    53  		// allocation free path for curves with a length that is a whole number of bytes
    54  		if len(hash) >= l {
    55  			// truncate hash
    56  			copy(dst, hash[:l])
    57  			return
    58  		}
    59  		// pad hash with leading zeros
    60  		p := l - len(hash)
    61  		for i := 0; i < p; i++ {
    62  			dst[i] = 0
    63  		}
    64  		copy(dst[p:], hash)
    65  		return
    66  	}
    67  	// TODO(mundaym): avoid hashToInt call here
    68  	hashToInt(hash, c).FillBytes(dst)
    69  }
    70  
    71  func sign(priv *PrivateKey, csprng *cipher.StreamReader, c elliptic.Curve, hash []byte) (r, s *big.Int, err error) {
    72  	if functionCode, blockSize, ok := canUseKDSA(c); ok {
    73  		for {
    74  			var k *big.Int
    75  			k, err = randFieldElement(c, *csprng)
    76  			if err != nil {
    77  				return nil, nil, err
    78  			}
    79  
    80  			// The parameter block looks like the following for sign.
    81  			// 	+---------------------+
    82  			// 	|   Signature(R)      |
    83  			//	+---------------------+
    84  			//	|   Signature(S)      |
    85  			//	+---------------------+
    86  			//	|   Hashed Message    |
    87  			//	+---------------------+
    88  			//	|   Private Key       |
    89  			//	+---------------------+
    90  			//	|   Random Number     |
    91  			//	+---------------------+
    92  			//	|                     |
    93  			//	|        ...          |
    94  			//	|                     |
    95  			//	+---------------------+
    96  			// The common components(signatureR, signatureS, hashedMessage, privateKey and
    97  			// random number) each takes block size of bytes. The block size is different for
    98  			// different curves and is set by canUseKDSA function.
    99  			var params [4096]byte
   100  
   101  			// Copy content into the parameter block. In the sign case,
   102  			// we copy hashed message, private key and random number into
   103  			// the parameter block.
   104  			hashToBytes(params[2*blockSize:3*blockSize], hash, c)
   105  			priv.D.FillBytes(params[3*blockSize : 4*blockSize])
   106  			k.FillBytes(params[4*blockSize : 5*blockSize])
   107  			// Convert verify function code into a sign function code by adding 8.
   108  			// We also need to set the 'deterministic' bit in the function code, by
   109  			// adding 128, in order to stop the instruction using its own random number
   110  			// generator in addition to the random number we supply.
   111  			switch kdsa(functionCode+136, &params) {
   112  			case 0: // success
   113  				r = new(big.Int)
   114  				r.SetBytes(params[:blockSize])
   115  				s = new(big.Int)
   116  				s.SetBytes(params[blockSize : 2*blockSize])
   117  				return
   118  			case 1: // error
   119  				return nil, nil, errZeroParam
   120  			case 2: // retry
   121  				continue
   122  			}
   123  			panic("unreachable")
   124  		}
   125  	}
   126  	return signGeneric(priv, csprng, c, hash)
   127  }
   128  
   129  func verify(pub *PublicKey, c elliptic.Curve, hash []byte, r, s *big.Int) bool {
   130  	if functionCode, blockSize, ok := canUseKDSA(c); ok {
   131  		// The parameter block looks like the following for verify:
   132  		// 	+---------------------+
   133  		// 	|   Signature(R)      |
   134  		//	+---------------------+
   135  		//	|   Signature(S)      |
   136  		//	+---------------------+
   137  		//	|   Hashed Message    |
   138  		//	+---------------------+
   139  		//	|   Public Key X      |
   140  		//	+---------------------+
   141  		//	|   Public Key Y      |
   142  		//	+---------------------+
   143  		//	|                     |
   144  		//	|        ...          |
   145  		//	|                     |
   146  		//	+---------------------+
   147  		// The common components(signatureR, signatureS, hashed message, public key X,
   148  		// and public key Y) each takes block size of bytes. The block size is different for
   149  		// different curves and is set by canUseKDSA function.
   150  		var params [4096]byte
   151  
   152  		// Copy content into the parameter block. In the verify case,
   153  		// we copy signature (r), signature(s), hashed message, public key x component,
   154  		// and public key y component into the parameter block.
   155  		r.FillBytes(params[0*blockSize : 1*blockSize])
   156  		s.FillBytes(params[1*blockSize : 2*blockSize])
   157  		hashToBytes(params[2*blockSize:3*blockSize], hash, c)
   158  		pub.X.FillBytes(params[3*blockSize : 4*blockSize])
   159  		pub.Y.FillBytes(params[4*blockSize : 5*blockSize])
   160  		return kdsa(functionCode, &params) == 0
   161  	}
   162  	return verifyGeneric(pub, c, hash, r, s)
   163  }
   164
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