golang.org/toolchain@v0.0.1-go1.9rc2.windows-amd64/src/vendor/golang_org/x/crypto/chacha20poly1305/chacha20poly1305.go (about)

     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  // Package chacha20poly1305 implements the ChaCha20-Poly1305 AEAD as specified in RFC 7539.
     6  package chacha20poly1305 // import "golang.org/x/crypto/chacha20poly1305"
     7  
     8  import (
     9  	"crypto/cipher"
    10  	"errors"
    11  )
    12  
    13  const (
    14  	// KeySize is the size of the key used by this AEAD, in bytes.
    15  	KeySize = 32
    16  	// NonceSize is the size of the nonce used with this AEAD, in bytes.
    17  	NonceSize = 12
    18  )
    19  
    20  type chacha20poly1305 struct {
    21  	key [32]byte
    22  }
    23  
    24  // New returns a ChaCha20-Poly1305 AEAD that uses the given, 256-bit key.
    25  func New(key []byte) (cipher.AEAD, error) {
    26  	if len(key) != KeySize {
    27  		return nil, errors.New("chacha20poly1305: bad key length")
    28  	}
    29  	ret := new(chacha20poly1305)
    30  	copy(ret.key[:], key)
    31  	return ret, nil
    32  }
    33  
    34  func (c *chacha20poly1305) NonceSize() int {
    35  	return NonceSize
    36  }
    37  
    38  func (c *chacha20poly1305) Overhead() int {
    39  	return 16
    40  }
    41  
    42  func (c *chacha20poly1305) Seal(dst, nonce, plaintext, additionalData []byte) []byte {
    43  	if len(nonce) != NonceSize {
    44  		panic("chacha20poly1305: bad nonce length passed to Seal")
    45  	}
    46  
    47  	if uint64(len(plaintext)) > (1<<38)-64 {
    48  		panic("chacha20poly1305: plaintext too large")
    49  	}
    50  
    51  	return c.seal(dst, nonce, plaintext, additionalData)
    52  }
    53  
    54  var errOpen = errors.New("chacha20poly1305: message authentication failed")
    55  
    56  func (c *chacha20poly1305) Open(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
    57  	if len(nonce) != NonceSize {
    58  		panic("chacha20poly1305: bad nonce length passed to Open")
    59  	}
    60  	if len(ciphertext) < 16 {
    61  		return nil, errOpen
    62  	}
    63  	if uint64(len(ciphertext)) > (1<<38)-48 {
    64  		panic("chacha20poly1305: ciphertext too large")
    65  	}
    66  
    67  	return c.open(dst, nonce, ciphertext, additionalData)
    68  }
    69  
    70  // sliceForAppend takes a slice and a requested number of bytes. It returns a
    71  // slice with the contents of the given slice followed by that many bytes and a
    72  // second slice that aliases into it and contains only the extra bytes. If the
    73  // original slice has sufficient capacity then no allocation is performed.
    74  func sliceForAppend(in []byte, n int) (head, tail []byte) {
    75  	if total := len(in) + n; cap(in) >= total {
    76  		head = in[:total]
    77  	} else {
    78  		head = make([]byte, total)
    79  		copy(head, in)
    80  	}
    81  	tail = head[len(in):]
    82  	return
    83  }