github.com/dorkamotorka/go/src@v0.0.0-20230614113921-187095f0e316/crypto/rsa/pkcs1v15.go (about)

     1  // Copyright 2009 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 rsa
     6  
     7  import (
     8  	"crypto"
     9  	"crypto/internal/boring"
    10  	"crypto/internal/randutil"
    11  	"crypto/subtle"
    12  	"errors"
    13  	"io"
    14  )
    15  
    16  // This file implements encryption and decryption using PKCS #1 v1.5 padding.
    17  
    18  // PKCS1v15DecryptOptions is for passing options to PKCS #1 v1.5 decryption using
    19  // the crypto.Decrypter interface.
    20  type PKCS1v15DecryptOptions struct {
    21  	// SessionKeyLen is the length of the session key that is being
    22  	// decrypted. If not zero, then a padding error during decryption will
    23  	// cause a random plaintext of this length to be returned rather than
    24  	// an error. These alternatives happen in constant time.
    25  	SessionKeyLen int
    26  }
    27  
    28  // EncryptPKCS1v15 encrypts the given message with RSA and the padding
    29  // scheme from PKCS #1 v1.5.  The message must be no longer than the
    30  // length of the public modulus minus 11 bytes.
    31  //
    32  // The random parameter is used as a source of entropy to ensure that
    33  // encrypting the same message twice doesn't result in the same
    34  // ciphertext.
    35  //
    36  // WARNING: use of this function to encrypt plaintexts other than
    37  // session keys is dangerous. Use RSA OAEP in new protocols.
    38  func EncryptPKCS1v15(random io.Reader, pub *PublicKey, msg []byte) ([]byte, error) {
    39  	randutil.MaybeReadByte(random)
    40  
    41  	if err := checkPub(pub); err != nil {
    42  		return nil, err
    43  	}
    44  	k := pub.Size()
    45  	if len(msg) > k-11 {
    46  		return nil, ErrMessageTooLong
    47  	}
    48  
    49  	if boring.Enabled && random == boring.RandReader {
    50  		bkey, err := boringPublicKey(pub)
    51  		if err != nil {
    52  			return nil, err
    53  		}
    54  		return boring.EncryptRSAPKCS1(bkey, msg)
    55  	}
    56  	boring.UnreachableExceptTests()
    57  
    58  	// EM = 0x00 || 0x02 || PS || 0x00 || M
    59  	em := make([]byte, k)
    60  	em[1] = 2
    61  	ps, mm := em[2:len(em)-len(msg)-1], em[len(em)-len(msg):]
    62  	err := nonZeroRandomBytes(ps, random)
    63  	if err != nil {
    64  		return nil, err
    65  	}
    66  	em[len(em)-len(msg)-1] = 0
    67  	copy(mm, msg)
    68  
    69  	if boring.Enabled {
    70  		var bkey *boring.PublicKeyRSA
    71  		bkey, err = boringPublicKey(pub)
    72  		if err != nil {
    73  			return nil, err
    74  		}
    75  		return boring.EncryptRSANoPadding(bkey, em)
    76  	}
    77  
    78  	return encrypt(pub, em)
    79  }
    80  
    81  // DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS #1 v1.5.
    82  // The random parameter is legacy and ignored, and it can be as nil.
    83  //
    84  // Note that whether this function returns an error or not discloses secret
    85  // information. If an attacker can cause this function to run repeatedly and
    86  // learn whether each instance returned an error then they can decrypt and
    87  // forge signatures as if they had the private key. See
    88  // DecryptPKCS1v15SessionKey for a way of solving this problem.
    89  func DecryptPKCS1v15(random io.Reader, priv *PrivateKey, ciphertext []byte) ([]byte, error) {
    90  	if err := checkPub(&priv.PublicKey); err != nil {
    91  		return nil, err
    92  	}
    93  
    94  	if boring.Enabled {
    95  		bkey, err := boringPrivateKey(priv)
    96  		if err != nil {
    97  			return nil, err
    98  		}
    99  		out, err := boring.DecryptRSAPKCS1(bkey, ciphertext)
   100  		if err != nil {
   101  			return nil, ErrDecryption
   102  		}
   103  		return out, nil
   104  	}
   105  
   106  	valid, out, index, err := decryptPKCS1v15(priv, ciphertext)
   107  	if err != nil {
   108  		return nil, err
   109  	}
   110  	if valid == 0 {
   111  		return nil, ErrDecryption
   112  	}
   113  	return out[index:], nil
   114  }
   115  
   116  // DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding
   117  // scheme from PKCS #1 v1.5. The random parameter is legacy and ignored, and it
   118  // can be nil.
   119  //
   120  // DecryptPKCS1v15SessionKey returns an error if the ciphertext is the wrong
   121  // length or if the ciphertext is greater than the public modulus. Otherwise, no
   122  // error is returned. If the padding is valid, the resulting plaintext message
   123  // is copied into key. Otherwise, key is unchanged. These alternatives occur in
   124  // constant time. It is intended that the user of this function generate a
   125  // random session key beforehand and continue the protocol with the resulting
   126  // value.
   127  //
   128  // Note that if the session key is too small then it may be possible for an
   129  // attacker to brute-force it. If they can do that then they can learn whether a
   130  // random value was used (because it'll be different for the same ciphertext)
   131  // and thus whether the padding was correct. This also defeats the point of this
   132  // function. Using at least a 16-byte key will protect against this attack.
   133  //
   134  // This method implements protections against Bleichenbacher chosen ciphertext
   135  // attacks [0] described in RFC 3218 Section 2.3.2 [1]. While these protections
   136  // make a Bleichenbacher attack significantly more difficult, the protections
   137  // are only effective if the rest of the protocol which uses
   138  // DecryptPKCS1v15SessionKey is designed with these considerations in mind. In
   139  // particular, if any subsequent operations which use the decrypted session key
   140  // leak any information about the key (e.g. whether it is a static or random
   141  // key) then the mitigations are defeated. This method must be used extremely
   142  // carefully, and typically should only be used when absolutely necessary for
   143  // compatibility with an existing protocol (such as TLS) that is designed with
   144  // these properties in mind.
   145  //
   146  //   - [0] “Chosen Ciphertext Attacks Against Protocols Based on the RSA Encryption
   147  //     Standard PKCS #1”, Daniel Bleichenbacher, Advances in Cryptology (Crypto '98)
   148  //   - [1] RFC 3218, Preventing the Million Message Attack on CMS,
   149  //     https://www.rfc-editor.org/rfc/rfc3218.html
   150  func DecryptPKCS1v15SessionKey(random io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) error {
   151  	if err := checkPub(&priv.PublicKey); err != nil {
   152  		return err
   153  	}
   154  	k := priv.Size()
   155  	if k-(len(key)+3+8) < 0 {
   156  		return ErrDecryption
   157  	}
   158  
   159  	valid, em, index, err := decryptPKCS1v15(priv, ciphertext)
   160  	if err != nil {
   161  		return err
   162  	}
   163  
   164  	if len(em) != k {
   165  		// This should be impossible because decryptPKCS1v15 always
   166  		// returns the full slice.
   167  		return ErrDecryption
   168  	}
   169  
   170  	valid &= subtle.ConstantTimeEq(int32(len(em)-index), int32(len(key)))
   171  	subtle.ConstantTimeCopy(valid, key, em[len(em)-len(key):])
   172  	return nil
   173  }
   174  
   175  // decryptPKCS1v15 decrypts ciphertext using priv. It returns one or zero in
   176  // valid that indicates whether the plaintext was correctly structured.
   177  // In either case, the plaintext is returned in em so that it may be read
   178  // independently of whether it was valid in order to maintain constant memory
   179  // access patterns. If the plaintext was valid then index contains the index of
   180  // the original message in em, to allow constant time padding removal.
   181  func decryptPKCS1v15(priv *PrivateKey, ciphertext []byte) (valid int, em []byte, index int, err error) {
   182  	k := priv.Size()
   183  	if k < 11 {
   184  		err = ErrDecryption
   185  		return
   186  	}
   187  
   188  	if boring.Enabled {
   189  		var bkey *boring.PrivateKeyRSA
   190  		bkey, err = boringPrivateKey(priv)
   191  		if err != nil {
   192  			return
   193  		}
   194  		em, err = boring.DecryptRSANoPadding(bkey, ciphertext)
   195  		if err != nil {
   196  			return
   197  		}
   198  	} else {
   199  		em, err = decrypt(priv, ciphertext, noCheck)
   200  		if err != nil {
   201  			return
   202  		}
   203  	}
   204  
   205  	firstByteIsZero := subtle.ConstantTimeByteEq(em[0], 0)
   206  	secondByteIsTwo := subtle.ConstantTimeByteEq(em[1], 2)
   207  
   208  	// The remainder of the plaintext must be a string of non-zero random
   209  	// octets, followed by a 0, followed by the message.
   210  	//   lookingForIndex: 1 iff we are still looking for the zero.
   211  	//   index: the offset of the first zero byte.
   212  	lookingForIndex := 1
   213  
   214  	for i := 2; i < len(em); i++ {
   215  		equals0 := subtle.ConstantTimeByteEq(em[i], 0)
   216  		index = subtle.ConstantTimeSelect(lookingForIndex&equals0, i, index)
   217  		lookingForIndex = subtle.ConstantTimeSelect(equals0, 0, lookingForIndex)
   218  	}
   219  
   220  	// The PS padding must be at least 8 bytes long, and it starts two
   221  	// bytes into em.
   222  	validPS := subtle.ConstantTimeLessOrEq(2+8, index)
   223  
   224  	valid = firstByteIsZero & secondByteIsTwo & (^lookingForIndex & 1) & validPS
   225  	index = subtle.ConstantTimeSelect(valid, index+1, 0)
   226  	return valid, em, index, nil
   227  }
   228  
   229  // nonZeroRandomBytes fills the given slice with non-zero random octets.
   230  func nonZeroRandomBytes(s []byte, random io.Reader) (err error) {
   231  	_, err = io.ReadFull(random, s)
   232  	if err != nil {
   233  		return
   234  	}
   235  
   236  	for i := 0; i < len(s); i++ {
   237  		for s[i] == 0 {
   238  			_, err = io.ReadFull(random, s[i:i+1])
   239  			if err != nil {
   240  				return
   241  			}
   242  			// In tests, the PRNG may return all zeros so we do
   243  			// this to break the loop.
   244  			s[i] ^= 0x42
   245  		}
   246  	}
   247  
   248  	return
   249  }
   250  
   251  // These are ASN1 DER structures:
   252  //
   253  //	DigestInfo ::= SEQUENCE {
   254  //	  digestAlgorithm AlgorithmIdentifier,
   255  //	  digest OCTET STRING
   256  //	}
   257  //
   258  // For performance, we don't use the generic ASN1 encoder. Rather, we
   259  // precompute a prefix of the digest value that makes a valid ASN1 DER string
   260  // with the correct contents.
   261  var hashPrefixes = map[crypto.Hash][]byte{
   262  	crypto.MD5:       {0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10},
   263  	crypto.SHA1:      {0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
   264  	crypto.SHA224:    {0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05, 0x00, 0x04, 0x1c},
   265  	crypto.SHA256:    {0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
   266  	crypto.SHA384:    {0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30},
   267  	crypto.SHA512:    {0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40},
   268  	crypto.MD5SHA1:   {}, // A special TLS case which doesn't use an ASN1 prefix.
   269  	crypto.RIPEMD160: {0x30, 0x20, 0x30, 0x08, 0x06, 0x06, 0x28, 0xcf, 0x06, 0x03, 0x00, 0x31, 0x04, 0x14},
   270  }
   271  
   272  // SignPKCS1v15 calculates the signature of hashed using
   273  // RSASSA-PKCS1-V1_5-SIGN from RSA PKCS #1 v1.5.  Note that hashed must
   274  // be the result of hashing the input message using the given hash
   275  // function. If hash is zero, hashed is signed directly. This isn't
   276  // advisable except for interoperability.
   277  //
   278  // The random parameter is legacy and ignored, and it can be as nil.
   279  //
   280  // This function is deterministic. Thus, if the set of possible
   281  // messages is small, an attacker may be able to build a map from
   282  // messages to signatures and identify the signed messages. As ever,
   283  // signatures provide authenticity, not confidentiality.
   284  func SignPKCS1v15(random io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) ([]byte, error) {
   285  	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
   286  	if err != nil {
   287  		return nil, err
   288  	}
   289  
   290  	tLen := len(prefix) + hashLen
   291  	k := priv.Size()
   292  	if k < tLen+11 {
   293  		return nil, ErrMessageTooLong
   294  	}
   295  
   296  	if boring.Enabled {
   297  		bkey, err := boringPrivateKey(priv)
   298  		if err != nil {
   299  			return nil, err
   300  		}
   301  		return boring.SignRSAPKCS1v15(bkey, hash, hashed)
   302  	}
   303  
   304  	// EM = 0x00 || 0x01 || PS || 0x00 || T
   305  	em := make([]byte, k)
   306  	em[1] = 1
   307  	for i := 2; i < k-tLen-1; i++ {
   308  		em[i] = 0xff
   309  	}
   310  	copy(em[k-tLen:k-hashLen], prefix)
   311  	copy(em[k-hashLen:k], hashed)
   312  
   313  	return decrypt(priv, em, withCheck)
   314  }
   315  
   316  // VerifyPKCS1v15 verifies an RSA PKCS #1 v1.5 signature.
   317  // hashed is the result of hashing the input message using the given hash
   318  // function and sig is the signature. A valid signature is indicated by
   319  // returning a nil error. If hash is zero then hashed is used directly. This
   320  // isn't advisable except for interoperability.
   321  func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) error {
   322  	if boring.Enabled {
   323  		bkey, err := boringPublicKey(pub)
   324  		if err != nil {
   325  			return err
   326  		}
   327  		if err := boring.VerifyRSAPKCS1v15(bkey, hash, hashed, sig); err != nil {
   328  			return ErrVerification
   329  		}
   330  		return nil
   331  	}
   332  
   333  	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
   334  	if err != nil {
   335  		return err
   336  	}
   337  
   338  	tLen := len(prefix) + hashLen
   339  	k := pub.Size()
   340  	if k < tLen+11 {
   341  		return ErrVerification
   342  	}
   343  
   344  	// RFC 8017 Section 8.2.2: If the length of the signature S is not k
   345  	// octets (where k is the length in octets of the RSA modulus n), output
   346  	// "invalid signature" and stop.
   347  	if k != len(sig) {
   348  		return ErrVerification
   349  	}
   350  
   351  	em, err := encrypt(pub, sig)
   352  	if err != nil {
   353  		return ErrVerification
   354  	}
   355  	// EM = 0x00 || 0x01 || PS || 0x00 || T
   356  
   357  	ok := subtle.ConstantTimeByteEq(em[0], 0)
   358  	ok &= subtle.ConstantTimeByteEq(em[1], 1)
   359  	ok &= subtle.ConstantTimeCompare(em[k-hashLen:k], hashed)
   360  	ok &= subtle.ConstantTimeCompare(em[k-tLen:k-hashLen], prefix)
   361  	ok &= subtle.ConstantTimeByteEq(em[k-tLen-1], 0)
   362  
   363  	for i := 2; i < k-tLen-1; i++ {
   364  		ok &= subtle.ConstantTimeByteEq(em[i], 0xff)
   365  	}
   366  
   367  	if ok != 1 {
   368  		return ErrVerification
   369  	}
   370  
   371  	return nil
   372  }
   373  
   374  func pkcs1v15HashInfo(hash crypto.Hash, inLen int) (hashLen int, prefix []byte, err error) {
   375  	// Special case: crypto.Hash(0) is used to indicate that the data is
   376  	// signed directly.
   377  	if hash == 0 {
   378  		return inLen, nil, nil
   379  	}
   380  
   381  	hashLen = hash.Size()
   382  	if inLen != hashLen {
   383  		return 0, nil, errors.New("crypto/rsa: input must be hashed message")
   384  	}
   385  	prefix, ok := hashPrefixes[hash]
   386  	if !ok {
   387  		return 0, nil, errors.New("crypto/rsa: unsupported hash function")
   388  	}
   389  	return
   390  }