mirror of https://github.com/cheat/cheat.git
92 lines
2.1 KiB
Go
92 lines
2.1 KiB
Go
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// Copyright 2017 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package encoding
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import (
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"io"
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"math/big"
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"math/bits"
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)
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// An MPI is used to store the contents of a big integer, along with the bit
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// length that was specified in the original input. This allows the MPI to be
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// reserialized exactly.
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type MPI struct {
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bytes []byte
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bitLength uint16
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}
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// NewMPI returns a MPI initialized with bytes.
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func NewMPI(bytes []byte) *MPI {
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for len(bytes) != 0 && bytes[0] == 0 {
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bytes = bytes[1:]
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}
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if len(bytes) == 0 {
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bitLength := uint16(0)
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return &MPI{bytes, bitLength}
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}
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bitLength := 8*uint16(len(bytes)-1) + uint16(bits.Len8(bytes[0]))
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return &MPI{bytes, bitLength}
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}
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// Bytes returns the decoded data.
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func (m *MPI) Bytes() []byte {
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return m.bytes
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}
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// BitLength is the size in bits of the decoded data.
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func (m *MPI) BitLength() uint16 {
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return m.bitLength
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}
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// EncodedBytes returns the encoded data.
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func (m *MPI) EncodedBytes() []byte {
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return append([]byte{byte(m.bitLength >> 8), byte(m.bitLength)}, m.bytes...)
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}
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// EncodedLength is the size in bytes of the encoded data.
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func (m *MPI) EncodedLength() uint16 {
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return uint16(2 + len(m.bytes))
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}
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// ReadFrom reads into m the next MPI from r.
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func (m *MPI) ReadFrom(r io.Reader) (int64, error) {
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var buf [2]byte
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n, err := io.ReadFull(r, buf[0:])
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if err != nil {
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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return int64(n), err
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}
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m.bitLength = uint16(buf[0])<<8 | uint16(buf[1])
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m.bytes = make([]byte, (int(m.bitLength)+7)/8)
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nn, err := io.ReadFull(r, m.bytes)
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if err == io.EOF {
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err = io.ErrUnexpectedEOF
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}
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// remove leading zero bytes from malformed GnuPG encoded MPIs:
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// https://bugs.gnupg.org/gnupg/issue1853
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// for _, b := range m.bytes {
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// if b != 0 {
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// break
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// }
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// m.bytes = m.bytes[1:]
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// m.bitLength -= 8
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// }
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return int64(n) + int64(nn), err
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}
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// SetBig initializes m with the bits from n.
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func (m *MPI) SetBig(n *big.Int) *MPI {
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m.bytes = n.Bytes()
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m.bitLength = uint16(n.BitLen())
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return m
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}
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