// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package rsa

import (
	
	
	
	
	

	
)

// This file implements encryption and decryption using PKCS #1 v1.5 padding.

// PKCS1v15DecrypterOpts is for passing options to PKCS #1 v1.5 decryption using
// the crypto.Decrypter interface.
type PKCS1v15DecryptOptions struct {
	// SessionKeyLen is the length of the session key that is being
	// decrypted. If not zero, then a padding error during decryption will
	// cause a random plaintext of this length to be returned rather than
	// an error. These alternatives happen in constant time.
	SessionKeyLen int
}

// EncryptPKCS1v15 encrypts the given message with RSA and the padding
// scheme from PKCS #1 v1.5.  The message must be no longer than the
// length of the public modulus minus 11 bytes.
//
// The rand parameter is used as a source of entropy to ensure that
// encrypting the same message twice doesn't result in the same
// ciphertext.
//
// WARNING: use of this function to encrypt plaintexts other than
// session keys is dangerous. Use RSA OAEP in new protocols.
func ( io.Reader,  *PublicKey,  []byte) ([]byte, error) {
	randutil.MaybeReadByte()

	if  := checkPub();  != nil {
		return nil, 
	}
	 := .Size()
	if len() > -11 {
		return nil, ErrMessageTooLong
	}

	// EM = 0x00 || 0x02 || PS || 0x00 || M
	 := make([]byte, )
	[1] = 2
	,  := [2:len()-len()-1], [len()-len():]
	 := nonZeroRandomBytes(, )
	if  != nil {
		return nil, 
	}
	[len()-len()-1] = 0
	copy(, )

	 := new(big.Int).SetBytes()
	 := encrypt(new(big.Int), , )

	return .FillBytes(), nil
}

// DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS #1 v1.5.
// If rand != nil, it uses RSA blinding to avoid timing side-channel attacks.
//
// Note that whether this function returns an error or not discloses secret
// information. If an attacker can cause this function to run repeatedly and
// learn whether each instance returned an error then they can decrypt and
// forge signatures as if they had the private key. See
// DecryptPKCS1v15SessionKey for a way of solving this problem.
func ( io.Reader,  *PrivateKey,  []byte) ([]byte, error) {
	if  := checkPub(&.PublicKey);  != nil {
		return nil, 
	}
	, , ,  := decryptPKCS1v15(, , )
	if  != nil {
		return nil, 
	}
	if  == 0 {
		return nil, ErrDecryption
	}
	return [:], nil
}

// DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding scheme from PKCS #1 v1.5.
// If rand != nil, it uses RSA blinding to avoid timing side-channel attacks.
// It returns an error if the ciphertext is the wrong length or if the
// ciphertext is greater than the public modulus. Otherwise, no error is
// returned. If the padding is valid, the resulting plaintext message is copied
// into key. Otherwise, key is unchanged. These alternatives occur in constant
// time. It is intended that the user of this function generate a random
// session key beforehand and continue the protocol with the resulting value.
// This will remove any possibility that an attacker can learn any information
// about the plaintext.
// See ``Chosen Ciphertext Attacks Against Protocols Based on the RSA
// Encryption Standard PKCS #1'', Daniel Bleichenbacher, Advances in Cryptology
// (Crypto '98).
//
// Note that if the session key is too small then it may be possible for an
// attacker to brute-force it. If they can do that then they can learn whether
// a random value was used (because it'll be different for the same ciphertext)
// and thus whether the padding was correct. This defeats the point of this
// function. Using at least a 16-byte key will protect against this attack.
func ( io.Reader,  *PrivateKey,  []byte,  []byte) error {
	if  := checkPub(&.PublicKey);  != nil {
		return 
	}
	 := .Size()
	if -(len()+3+8) < 0 {
		return ErrDecryption
	}

	, , ,  := decryptPKCS1v15(, , )
	if  != nil {
		return 
	}

	if len() !=  {
		// This should be impossible because decryptPKCS1v15 always
		// returns the full slice.
		return ErrDecryption
	}

	 &= subtle.ConstantTimeEq(int32(len()-), int32(len()))
	subtle.ConstantTimeCopy(, , [len()-len():])
	return nil
}

// decryptPKCS1v15 decrypts ciphertext using priv and blinds the operation if
// rand is not nil. It returns one or zero in valid that indicates whether the
// plaintext was correctly structured. In either case, the plaintext is
// returned in em so that it may be read independently of whether it was valid
// in order to maintain constant memory access patterns. If the plaintext was
// valid then index contains the index of the original message in em.
func decryptPKCS1v15( io.Reader,  *PrivateKey,  []byte) ( int,  []byte,  int,  error) {
	 := .Size()
	if  < 11 {
		 = ErrDecryption
		return
	}

	 := new(big.Int).SetBytes()
	,  := decrypt(, , )
	if  != nil {
		return
	}

	 = .FillBytes(make([]byte, ))
	 := subtle.ConstantTimeByteEq([0], 0)
	 := subtle.ConstantTimeByteEq([1], 2)

	// The remainder of the plaintext must be a string of non-zero random
	// octets, followed by a 0, followed by the message.
	//   lookingForIndex: 1 iff we are still looking for the zero.
	//   index: the offset of the first zero byte.
	 := 1

	for  := 2;  < len(); ++ {
		 := subtle.ConstantTimeByteEq([], 0)
		 = subtle.ConstantTimeSelect(&, , )
		 = subtle.ConstantTimeSelect(, 0, )
	}

	// The PS padding must be at least 8 bytes long, and it starts two
	// bytes into em.
	 := subtle.ConstantTimeLessOrEq(2+8, )

	 =  &  & (^ & 1) & 
	 = subtle.ConstantTimeSelect(, +1, 0)
	return , , , nil
}

// nonZeroRandomBytes fills the given slice with non-zero random octets.
func nonZeroRandomBytes( []byte,  io.Reader) ( error) {
	_,  = io.ReadFull(, )
	if  != nil {
		return
	}

	for  := 0;  < len(); ++ {
		for [] == 0 {
			_,  = io.ReadFull(, [:+1])
			if  != nil {
				return
			}
			// In tests, the PRNG may return all zeros so we do
			// this to break the loop.
			[] ^= 0x42
		}
	}

	return
}

// These are ASN1 DER structures:
//   DigestInfo ::= SEQUENCE {
//     digestAlgorithm AlgorithmIdentifier,
//     digest OCTET STRING
//   }
// For performance, we don't use the generic ASN1 encoder. Rather, we
// precompute a prefix of the digest value that makes a valid ASN1 DER string
// with the correct contents.
var hashPrefixes = map[crypto.Hash][]byte{
	crypto.MD5:       {0x30, 0x20, 0x30, 0x0c, 0x06, 0x08, 0x2a, 0x86, 0x48, 0x86, 0xf7, 0x0d, 0x02, 0x05, 0x05, 0x00, 0x04, 0x10},
	crypto.SHA1:      {0x30, 0x21, 0x30, 0x09, 0x06, 0x05, 0x2b, 0x0e, 0x03, 0x02, 0x1a, 0x05, 0x00, 0x04, 0x14},
	crypto.SHA224:    {0x30, 0x2d, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x04, 0x05, 0x00, 0x04, 0x1c},
	crypto.SHA256:    {0x30, 0x31, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x01, 0x05, 0x00, 0x04, 0x20},
	crypto.SHA384:    {0x30, 0x41, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x02, 0x05, 0x00, 0x04, 0x30},
	crypto.SHA512:    {0x30, 0x51, 0x30, 0x0d, 0x06, 0x09, 0x60, 0x86, 0x48, 0x01, 0x65, 0x03, 0x04, 0x02, 0x03, 0x05, 0x00, 0x04, 0x40},
	crypto.MD5SHA1:   {}, // A special TLS case which doesn't use an ASN1 prefix.
	crypto.RIPEMD160: {0x30, 0x20, 0x30, 0x08, 0x06, 0x06, 0x28, 0xcf, 0x06, 0x03, 0x00, 0x31, 0x04, 0x14},
}

// SignPKCS1v15 calculates the signature of hashed using
// RSASSA-PKCS1-V1_5-SIGN from RSA PKCS #1 v1.5.  Note that hashed must
// be the result of hashing the input message using the given hash
// function. If hash is zero, hashed is signed directly. This isn't
// advisable except for interoperability.
//
// If rand is not nil then RSA blinding will be used to avoid timing
// side-channel attacks.
//
// This function is deterministic. Thus, if the set of possible
// messages is small, an attacker may be able to build a map from
// messages to signatures and identify the signed messages. As ever,
// signatures provide authenticity, not confidentiality.
func ( io.Reader,  *PrivateKey,  crypto.Hash,  []byte) ([]byte, error) {
	, ,  := pkcs1v15HashInfo(, len())
	if  != nil {
		return nil, 
	}

	 := len() + 
	 := .Size()
	if  < +11 {
		return nil, ErrMessageTooLong
	}

	// EM = 0x00 || 0x01 || PS || 0x00 || T
	 := make([]byte, )
	[1] = 1
	for  := 2;  < --1; ++ {
		[] = 0xff
	}
	copy([-:-], )
	copy([-:], )

	 := new(big.Int).SetBytes()
	,  := decryptAndCheck(, , )
	if  != nil {
		return nil, 
	}

	return .FillBytes(), nil
}

// VerifyPKCS1v15 verifies an RSA PKCS #1 v1.5 signature.
// hashed is the result of hashing the input message using the given hash
// function and sig is the signature. A valid signature is indicated by
// returning a nil error. If hash is zero then hashed is used directly. This
// isn't advisable except for interoperability.
func ( *PublicKey,  crypto.Hash,  []byte,  []byte) error {
	, ,  := pkcs1v15HashInfo(, len())
	if  != nil {
		return 
	}

	 := len() + 
	 := .Size()
	if  < +11 {
		return ErrVerification
	}

	// RFC 8017 Section 8.2.2: If the length of the signature S is not k
	// octets (where k is the length in octets of the RSA modulus n), output
	// "invalid signature" and stop.
	if  != len() {
		return ErrVerification
	}

	 := new(big.Int).SetBytes()
	 := encrypt(new(big.Int), , )
	 := .FillBytes(make([]byte, ))
	// EM = 0x00 || 0x01 || PS || 0x00 || T

	 := subtle.ConstantTimeByteEq([0], 0)
	 &= subtle.ConstantTimeByteEq([1], 1)
	 &= subtle.ConstantTimeCompare([-:], )
	 &= subtle.ConstantTimeCompare([-:-], )
	 &= subtle.ConstantTimeByteEq([--1], 0)

	for  := 2;  < --1; ++ {
		 &= subtle.ConstantTimeByteEq([], 0xff)
	}

	if  != 1 {
		return ErrVerification
	}

	return nil
}

func pkcs1v15HashInfo( crypto.Hash,  int) ( int,  []byte,  error) {
	// Special case: crypto.Hash(0) is used to indicate that the data is
	// signed directly.
	if  == 0 {
		return , nil, nil
	}

	 = .Size()
	if  !=  {
		return 0, nil, errors.New("crypto/rsa: input must be hashed message")
	}
	,  := hashPrefixes[]
	if ! {
		return 0, nil, errors.New("crypto/rsa: unsupported hash function")
	}
	return
}