concat_kdf.go

Documentation: gopkg.in/go-jose/go-jose.v2/cipher

     1  /*-
     2   * Copyright 2014 Square Inc.
     3   *
     4   * Licensed under the Apache License, Version 2.0 (the "License");
     5   * you may not use this file except in compliance with the License.
     6   * You may obtain a copy of the License at
     7   *
     8   *     http://www.apache.org/licenses/LICENSE-2.0
     9   *
    10   * Unless required by applicable law or agreed to in writing, software
    11   * distributed under the License is distributed on an "AS IS" BASIS,
    12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13   * See the License for the specific language governing permissions and
    14   * limitations under the License.
    15   */
    16  
    17  package josecipher
    18  
    19  import (
    20  	"crypto"
    21  	"encoding/binary"
    22  	"hash"
    23  	"io"
    24  )
    25  
    26  type concatKDF struct {
    27  	z, info []byte
    28  	i       uint32
    29  	cache   []byte
    30  	hasher  hash.Hash
    31  }
    32  
    33  // NewConcatKDF builds a KDF reader based on the given inputs.
    34  func NewConcatKDF(hash crypto.Hash, z, algID, ptyUInfo, ptyVInfo, supPubInfo, supPrivInfo []byte) io.Reader {
    35  	buffer := make([]byte, uint64(len(algID))+uint64(len(ptyUInfo))+uint64(len(ptyVInfo))+uint64(len(supPubInfo))+uint64(len(supPrivInfo)))
    36  	n := 0
    37  	n += copy(buffer, algID)
    38  	n += copy(buffer[n:], ptyUInfo)
    39  	n += copy(buffer[n:], ptyVInfo)
    40  	n += copy(buffer[n:], supPubInfo)
    41  	copy(buffer[n:], supPrivInfo)
    42  
    43  	hasher := hash.New()
    44  
    45  	return &concatKDF{
    46  		z:      z,
    47  		info:   buffer,
    48  		hasher: hasher,
    49  		cache:  []byte{},
    50  		i:      1,
    51  	}
    52  }
    53  
    54  func (ctx *concatKDF) Read(out []byte) (int, error) {
    55  	copied := copy(out, ctx.cache)
    56  	ctx.cache = ctx.cache[copied:]
    57  
    58  	for copied < len(out) {
    59  		ctx.hasher.Reset()
    60  
    61  		// Write on a hash.Hash never fails
    62  		_ = binary.Write(ctx.hasher, binary.BigEndian, ctx.i)
    63  		_, _ = ctx.hasher.Write(ctx.z)
    64  		_, _ = ctx.hasher.Write(ctx.info)
    65  
    66  		hash := ctx.hasher.Sum(nil)
    67  		chunkCopied := copy(out[copied:], hash)
    68  		copied += chunkCopied
    69  		ctx.cache = hash[chunkCopied:]
    70  
    71  		ctx.i++
    72  	}
    73  
    74  	return copied, nil
    75  }
    76
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