peridot/vendor/github.com/ProtonMail/go-crypto/openpgp/internal/encoding/mpi.go
2022-07-07 22:13:21 +02:00

92 lines
2.1 KiB
Go

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