gcm_s390x.go

     1  // Copyright 2016 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  //go:build !purego
     6  
     7  package aes
     8  
     9  import (
    10  	"crypto/cipher"
    11  	"crypto/internal/alias"
    12  	"crypto/subtle"
    13  	"errors"
    14  	"internal/byteorder"
    15  	"internal/cpu"
    16  )
    17  
    18  // This file contains two implementations of AES-GCM. The first implementation
    19  // (gcmAsm) uses the KMCTR instruction to encrypt using AES in counter mode and
    20  // the KIMD instruction for GHASH. The second implementation (gcmKMA) uses the
    21  // newer KMA instruction which performs both operations.
    22  
    23  // gcmCount represents a 16-byte big-endian count value.
    24  type gcmCount [16]byte
    25  
    26  // inc increments the rightmost 32-bits of the count value by 1.
    27  func (x *gcmCount) inc() {
    28  	byteorder.BePutUint32(x[len(x)-4:], byteorder.BeUint32(x[len(x)-4:])+1)
    29  }
    30  
    31  // gcmLengths writes len0 || len1 as big-endian values to a 16-byte array.
    32  func gcmLengths(len0, len1 uint64) [16]byte {
    33  	v := [16]byte{}
    34  	byteorder.BePutUint64(v[0:], len0)
    35  	byteorder.BePutUint64(v[8:], len1)
    36  	return v
    37  }
    38  
    39  // gcmHashKey represents the 16-byte hash key required by the GHASH algorithm.
    40  type gcmHashKey [16]byte
    41  
    42  type gcmAsm struct {
    43  	block     *aesCipherAsm
    44  	hashKey   gcmHashKey
    45  	nonceSize int
    46  	tagSize   int
    47  }
    48  
    49  const (
    50  	gcmBlockSize         = 16
    51  	gcmTagSize           = 16
    52  	gcmMinimumTagSize    = 12 // NIST SP 800-38D recommends tags with 12 or more bytes.
    53  	gcmStandardNonceSize = 12
    54  )
    55  
    56  var errOpen = errors.New("cipher: message authentication failed")
    57  
    58  // Assert that aesCipherAsm implements the gcmAble interface.
    59  var _ gcmAble = (*aesCipherAsm)(nil)
    60  
    61  // NewGCM returns the AES cipher wrapped in Galois Counter Mode. This is only
    62  // called by [crypto/cipher.NewGCM] via the gcmAble interface.
    63  func (c *aesCipherAsm) NewGCM(nonceSize, tagSize int) (cipher.AEAD, error) {
    64  	var hk gcmHashKey
    65  	c.Encrypt(hk[:], hk[:])
    66  	g := gcmAsm{
    67  		block:     c,
    68  		hashKey:   hk,
    69  		nonceSize: nonceSize,
    70  		tagSize:   tagSize,
    71  	}
    72  	if cpu.S390X.HasAESGCM {
    73  		g := gcmKMA{g}
    74  		return &g, nil
    75  	}
    76  	return &g, nil
    77  }
    78  
    79  func (g *gcmAsm) NonceSize() int {
    80  	return g.nonceSize
    81  }
    82  
    83  func (g *gcmAsm) Overhead() int {
    84  	return g.tagSize
    85  }
    86  
    87  // sliceForAppend takes a slice and a requested number of bytes. It returns a
    88  // slice with the contents of the given slice followed by that many bytes and a
    89  // second slice that aliases into it and contains only the extra bytes. If the
    90  // original slice has sufficient capacity then no allocation is performed.
    91  func sliceForAppend(in []byte, n int) (head, tail []byte) {
    92  	if total := len(in) + n; cap(in) >= total {
    93  		head = in[:total]
    94  	} else {
    95  		head = make([]byte, total)
    96  		copy(head, in)
    97  	}
    98  	tail = head[len(in):]
    99  	return
   100  }
   101  
   102  // ghash uses the GHASH algorithm to hash data with the given key. The initial
   103  // hash value is given by hash which will be updated with the new hash value.
   104  // The length of data must be a multiple of 16-bytes.
   105  //
   106  //go:noescape
   107  func ghash(key *gcmHashKey, hash *[16]byte, data []byte)
   108  
   109  // paddedGHASH pads data with zeroes until its length is a multiple of
   110  // 16-bytes. It then calculates a new value for hash using the GHASH algorithm.
   111  func (g *gcmAsm) paddedGHASH(hash *[16]byte, data []byte) {
   112  	siz := len(data) &^ 0xf // align size to 16-bytes
   113  	if siz > 0 {
   114  		ghash(&g.hashKey, hash, data[:siz])
   115  		data = data[siz:]
   116  	}
   117  	if len(data) > 0 {
   118  		var s [16]byte
   119  		copy(s[:], data)
   120  		ghash(&g.hashKey, hash, s[:])
   121  	}
   122  }
   123  
   124  // cryptBlocksGCM encrypts src using AES in counter mode using the given
   125  // function code and key. The rightmost 32-bits of the counter are incremented
   126  // between each block as required by the GCM spec. The initial counter value
   127  // is given by cnt, which is updated with the value of the next counter value
   128  // to use.
   129  //
   130  // The lengths of both dst and buf must be greater than or equal to the length
   131  // of src. buf may be partially or completely overwritten during the execution
   132  // of the function.
   133  //
   134  //go:noescape
   135  func cryptBlocksGCM(fn code, key, dst, src, buf []byte, cnt *gcmCount)
   136  
   137  // counterCrypt encrypts src using AES in counter mode and places the result
   138  // into dst. cnt is the initial count value and will be updated with the next
   139  // count value. The length of dst must be greater than or equal to the length
   140  // of src.
   141  func (g *gcmAsm) counterCrypt(dst, src []byte, cnt *gcmCount) {
   142  	// Copying src into a buffer improves performance on some models when
   143  	// src and dst point to the same underlying array. We also need a
   144  	// buffer for counter values.
   145  	var ctrbuf, srcbuf [2048]byte
   146  	for len(src) >= 16 {
   147  		siz := len(src)
   148  		if len(src) > len(ctrbuf) {
   149  			siz = len(ctrbuf)
   150  		}
   151  		siz &^= 0xf // align siz to 16-bytes
   152  		copy(srcbuf[:], src[:siz])
   153  		cryptBlocksGCM(g.block.function, g.block.key, dst[:siz], srcbuf[:siz], ctrbuf[:], cnt)
   154  		src = src[siz:]
   155  		dst = dst[siz:]
   156  	}
   157  	if len(src) > 0 {
   158  		var x [16]byte
   159  		g.block.Encrypt(x[:], cnt[:])
   160  		for i := range src {
   161  			dst[i] = src[i] ^ x[i]
   162  		}
   163  		cnt.inc()
   164  	}
   165  }
   166  
   167  // deriveCounter computes the initial GCM counter state from the given nonce.
   168  // See NIST SP 800-38D, section 7.1.
   169  func (g *gcmAsm) deriveCounter(nonce []byte) gcmCount {
   170  	// GCM has two modes of operation with respect to the initial counter
   171  	// state: a "fast path" for 96-bit (12-byte) nonces, and a "slow path"
   172  	// for nonces of other lengths. For a 96-bit nonce, the nonce, along
   173  	// with a four-byte big-endian counter starting at one, is used
   174  	// directly as the starting counter. For other nonce sizes, the counter
   175  	// is computed by passing it through the GHASH function.
   176  	var counter gcmCount
   177  	if len(nonce) == gcmStandardNonceSize {
   178  		copy(counter[:], nonce)
   179  		counter[gcmBlockSize-1] = 1
   180  	} else {
   181  		var hash [16]byte
   182  		g.paddedGHASH(&hash, nonce)
   183  		lens := gcmLengths(0, uint64(len(nonce))*8)
   184  		g.paddedGHASH(&hash, lens[:])
   185  		copy(counter[:], hash[:])
   186  	}
   187  	return counter
   188  }
   189  
   190  // auth calculates GHASH(ciphertext, additionalData), masks the result with
   191  // tagMask and writes the result to out.
   192  func (g *gcmAsm) auth(out, ciphertext, additionalData []byte, tagMask *[gcmTagSize]byte) {
   193  	var hash [16]byte
   194  	g.paddedGHASH(&hash, additionalData)
   195  	g.paddedGHASH(&hash, ciphertext)
   196  	lens := gcmLengths(uint64(len(additionalData))*8, uint64(len(ciphertext))*8)
   197  	g.paddedGHASH(&hash, lens[:])
   198  
   199  	copy(out, hash[:])
   200  	for i := range out {
   201  		out[i] ^= tagMask[i]
   202  	}
   203  }
   204  
   205  // Seal encrypts and authenticates plaintext. See the [cipher.AEAD] interface for
   206  // details.
   207  func (g *gcmAsm) Seal(dst, nonce, plaintext, data []byte) []byte {
   208  	if len(nonce) != g.nonceSize {
   209  		panic("crypto/cipher: incorrect nonce length given to GCM")
   210  	}
   211  	if uint64(len(plaintext)) > ((1<<32)-2)*BlockSize {
   212  		panic("crypto/cipher: message too large for GCM")
   213  	}
   214  
   215  	ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
   216  	if alias.InexactOverlap(out[:len(plaintext)], plaintext) {
   217  		panic("crypto/cipher: invalid buffer overlap")
   218  	}
   219  
   220  	counter := g.deriveCounter(nonce)
   221  
   222  	var tagMask [gcmBlockSize]byte
   223  	g.block.Encrypt(tagMask[:], counter[:])
   224  	counter.inc()
   225  
   226  	var tagOut [gcmTagSize]byte
   227  	g.counterCrypt(out, plaintext, &counter)
   228  	g.auth(tagOut[:], out[:len(plaintext)], data, &tagMask)
   229  	copy(out[len(plaintext):], tagOut[:])
   230  
   231  	return ret
   232  }
   233  
   234  // Open authenticates and decrypts ciphertext. See the [cipher.AEAD] interface
   235  // for details.
   236  func (g *gcmAsm) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
   237  	if len(nonce) != g.nonceSize {
   238  		panic("crypto/cipher: incorrect nonce length given to GCM")
   239  	}
   240  	// Sanity check to prevent the authentication from always succeeding if an implementation
   241  	// leaves tagSize uninitialized, for example.
   242  	if g.tagSize < gcmMinimumTagSize {
   243  		panic("crypto/cipher: incorrect GCM tag size")
   244  	}
   245  	if len(ciphertext) < g.tagSize {
   246  		return nil, errOpen
   247  	}
   248  	if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
   249  		return nil, errOpen
   250  	}
   251  
   252  	tag := ciphertext[len(ciphertext)-g.tagSize:]
   253  	ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
   254  
   255  	counter := g.deriveCounter(nonce)
   256  
   257  	var tagMask [gcmBlockSize]byte
   258  	g.block.Encrypt(tagMask[:], counter[:])
   259  	counter.inc()
   260  
   261  	var expectedTag [gcmTagSize]byte
   262  	g.auth(expectedTag[:], ciphertext, data, &tagMask)
   263  
   264  	ret, out := sliceForAppend(dst, len(ciphertext))
   265  	if alias.InexactOverlap(out, ciphertext) {
   266  		panic("crypto/cipher: invalid buffer overlap")
   267  	}
   268  
   269  	if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
   270  		// The AESNI code decrypts and authenticates concurrently, and
   271  		// so overwrites dst in the event of a tag mismatch. That
   272  		// behavior is mimicked here in order to be consistent across
   273  		// platforms.
   274  		clear(out)
   275  		return nil, errOpen
   276  	}
   277  
   278  	g.counterCrypt(out, ciphertext, &counter)
   279  	return ret, nil
   280  }
   281  
   282  // gcmKMA implements the cipher.AEAD interface using the KMA instruction. It should
   283  // only be used if hasKMA is true.
   284  type gcmKMA struct {
   285  	gcmAsm
   286  }
   287  
   288  // flags for the KMA instruction
   289  const (
   290  	kmaHS      = 1 << 10 // hash subkey supplied
   291  	kmaLAAD    = 1 << 9  // last series of additional authenticated data
   292  	kmaLPC     = 1 << 8  // last series of plaintext or ciphertext blocks
   293  	kmaDecrypt = 1 << 7  // decrypt
   294  )
   295  
   296  // kmaGCM executes the encryption or decryption operation given by fn. The tag
   297  // will be calculated and written to tag. cnt should contain the current
   298  // counter state and will be overwritten with the updated counter state.
   299  // TODO(mundaym): could pass in hash subkey
   300  //
   301  //go:noescape
   302  func kmaGCM(fn code, key, dst, src, aad []byte, tag *[16]byte, cnt *gcmCount)
   303  
   304  // Seal encrypts and authenticates plaintext. See the [cipher.AEAD] interface for
   305  // details.
   306  func (g *gcmKMA) Seal(dst, nonce, plaintext, data []byte) []byte {
   307  	if len(nonce) != g.nonceSize {
   308  		panic("crypto/cipher: incorrect nonce length given to GCM")
   309  	}
   310  	if uint64(len(plaintext)) > ((1<<32)-2)*BlockSize {
   311  		panic("crypto/cipher: message too large for GCM")
   312  	}
   313  
   314  	ret, out := sliceForAppend(dst, len(plaintext)+g.tagSize)
   315  	if alias.InexactOverlap(out[:len(plaintext)], plaintext) {
   316  		panic("crypto/cipher: invalid buffer overlap")
   317  	}
   318  
   319  	counter := g.deriveCounter(nonce)
   320  	fc := g.block.function | kmaLAAD | kmaLPC
   321  
   322  	var tag [gcmTagSize]byte
   323  	kmaGCM(fc, g.block.key, out[:len(plaintext)], plaintext, data, &tag, &counter)
   324  	copy(out[len(plaintext):], tag[:])
   325  
   326  	return ret
   327  }
   328  
   329  // Open authenticates and decrypts ciphertext. See the [cipher.AEAD] interface
   330  // for details.
   331  func (g *gcmKMA) Open(dst, nonce, ciphertext, data []byte) ([]byte, error) {
   332  	if len(nonce) != g.nonceSize {
   333  		panic("crypto/cipher: incorrect nonce length given to GCM")
   334  	}
   335  	if len(ciphertext) < g.tagSize {
   336  		return nil, errOpen
   337  	}
   338  	if uint64(len(ciphertext)) > ((1<<32)-2)*uint64(BlockSize)+uint64(g.tagSize) {
   339  		return nil, errOpen
   340  	}
   341  
   342  	tag := ciphertext[len(ciphertext)-g.tagSize:]
   343  	ciphertext = ciphertext[:len(ciphertext)-g.tagSize]
   344  	ret, out := sliceForAppend(dst, len(ciphertext))
   345  	if alias.InexactOverlap(out, ciphertext) {
   346  		panic("crypto/cipher: invalid buffer overlap")
   347  	}
   348  
   349  	if g.tagSize < gcmMinimumTagSize {
   350  		panic("crypto/cipher: incorrect GCM tag size")
   351  	}
   352  
   353  	counter := g.deriveCounter(nonce)
   354  	fc := g.block.function | kmaLAAD | kmaLPC | kmaDecrypt
   355  
   356  	var expectedTag [gcmTagSize]byte
   357  	kmaGCM(fc, g.block.key, out[:len(ciphertext)], ciphertext, data, &expectedTag, &counter)
   358  
   359  	if subtle.ConstantTimeCompare(expectedTag[:g.tagSize], tag) != 1 {
   360  		// The AESNI code decrypts and authenticates concurrently, and
   361  		// so overwrites dst in the event of a tag mismatch. That
   362  		// behavior is mimicked here in order to be consistent across
   363  		// platforms.
   364  		clear(out)
   365  		return nil, errOpen
   366  	}
   367  
   368  	return ret, nil
   369  }
   370
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