Source file src/pkg/vendor/golang.org/x/crypto/chacha20poly1305/chacha20poly1305_generic.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	package chacha20poly1305
     6	
     7	import (
     8		"encoding/binary"
     9	
    10		"golang.org/x/crypto/internal/chacha20"
    11		"golang.org/x/crypto/internal/subtle"
    12		"golang.org/x/crypto/poly1305"
    13	)
    14	
    15	func roundTo16(n int) int {
    16		return 16 * ((n + 15) / 16)
    17	}
    18	
    19	func (c *chacha20poly1305) sealGeneric(dst, nonce, plaintext, additionalData []byte) []byte {
    20		ret, out := sliceForAppend(dst, len(plaintext)+poly1305.TagSize)
    21		if subtle.InexactOverlap(out, plaintext) {
    22			panic("chacha20poly1305: invalid buffer overlap")
    23		}
    24	
    25		var polyKey [32]byte
    26		s := chacha20.New(c.key, [3]uint32{
    27			binary.LittleEndian.Uint32(nonce[0:4]),
    28			binary.LittleEndian.Uint32(nonce[4:8]),
    29			binary.LittleEndian.Uint32(nonce[8:12]),
    30		})
    31		s.XORKeyStream(polyKey[:], polyKey[:])
    32		s.Advance() // skip the next 32 bytes
    33		s.XORKeyStream(out, plaintext)
    34	
    35		polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(plaintext))+8+8)
    36		copy(polyInput, additionalData)
    37		copy(polyInput[roundTo16(len(additionalData)):], out[:len(plaintext)])
    38		binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
    39		binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(plaintext)))
    40	
    41		var tag [poly1305.TagSize]byte
    42		poly1305.Sum(&tag, polyInput, &polyKey)
    43		copy(out[len(plaintext):], tag[:])
    44	
    45		return ret
    46	}
    47	
    48	func (c *chacha20poly1305) openGeneric(dst, nonce, ciphertext, additionalData []byte) ([]byte, error) {
    49		var tag [poly1305.TagSize]byte
    50		copy(tag[:], ciphertext[len(ciphertext)-16:])
    51		ciphertext = ciphertext[:len(ciphertext)-16]
    52	
    53		var polyKey [32]byte
    54		s := chacha20.New(c.key, [3]uint32{
    55			binary.LittleEndian.Uint32(nonce[0:4]),
    56			binary.LittleEndian.Uint32(nonce[4:8]),
    57			binary.LittleEndian.Uint32(nonce[8:12]),
    58		})
    59		s.XORKeyStream(polyKey[:], polyKey[:])
    60		s.Advance() // skip the next 32 bytes
    61	
    62		polyInput := make([]byte, roundTo16(len(additionalData))+roundTo16(len(ciphertext))+8+8)
    63		copy(polyInput, additionalData)
    64		copy(polyInput[roundTo16(len(additionalData)):], ciphertext)
    65		binary.LittleEndian.PutUint64(polyInput[len(polyInput)-16:], uint64(len(additionalData)))
    66		binary.LittleEndian.PutUint64(polyInput[len(polyInput)-8:], uint64(len(ciphertext)))
    67	
    68		ret, out := sliceForAppend(dst, len(ciphertext))
    69		if subtle.InexactOverlap(out, ciphertext) {
    70			panic("chacha20poly1305: invalid buffer overlap")
    71		}
    72		if !poly1305.Verify(&tag, polyInput, &polyKey) {
    73			for i := range out {
    74				out[i] = 0
    75			}
    76			return nil, errOpen
    77		}
    78	
    79		s.XORKeyStream(out, ciphertext)
    80		return ret, nil
    81	}
    82	

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