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/*-
* Copyright 2014 Square Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package josecipher
import (
"crypto"
"encoding/binary"
"hash"
"io"
)
type concatKDF struct {
z, info []byte
i uint32
cache []byte
hasher hash.Hash
}
// NewConcatKDF builds a KDF reader based on the given inputs.
func NewConcatKDF(hash crypto.Hash, z, algID, ptyUInfo, ptyVInfo, supPubInfo, supPrivInfo []byte) io.Reader {
buffer := make([]byte, uint64(len(algID))+uint64(len(ptyUInfo))+uint64(len(ptyVInfo))+uint64(len(supPubInfo))+uint64(len(supPrivInfo)))
n := 0
n += copy(buffer, algID)
n += copy(buffer[n:], ptyUInfo)
n += copy(buffer[n:], ptyVInfo)
n += copy(buffer[n:], supPubInfo)
copy(buffer[n:], supPrivInfo)
hasher := hash.New()
return &concatKDF{
z: z,
info: buffer,
hasher: hasher,
cache: []byte{},
i: 1,
}
}
func (ctx *concatKDF) Read(out []byte) (int, error) {
copied := copy(out, ctx.cache)
ctx.cache = ctx.cache[copied:]
for copied < len(out) {
ctx.hasher.Reset()
// Write on a hash.Hash never fails
_ = binary.Write(ctx.hasher, binary.BigEndian, ctx.i)
_, _ = ctx.hasher.Write(ctx.z)
_, _ = ctx.hasher.Write(ctx.info)
hash := ctx.hasher.Sum(nil)
chunkCopied := copy(out[copied:], hash)
copied += chunkCopied
ctx.cache = hash[chunkCopied:]
ctx.i++
}
return copied, nil
}
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