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package ct
// This file contains selectively chosen snippets of
// github.com/google/certificate-transparency-go@ 5cfe585726ad9d990d4db524d6ce2567b13e2f80
//
// These snippets only perform deserialization for SCTs and are recreated here to prevent pulling in the whole of the ct
// which contains yet another version of x509,asn1 and tls
import (
"encoding/binary"
"errors"
"fmt"
"io"
)
// Variable size structure prefix-header byte lengths
const (
CertificateLengthBytes = 3
PreCertificateLengthBytes = 3
ExtensionsLengthBytes = 2
CertificateChainLengthBytes = 3
SignatureLengthBytes = 2
)
func writeUint(w io.Writer, value uint64, numBytes int) error {
buf := make([]uint8, numBytes)
for i := 0; i < numBytes; i++ {
buf[numBytes-i-1] = uint8(value & 0xff)
value >>= 8
}
if value != 0 {
return errors.New("numBytes was insufficiently large to represent value")
}
if _, err := w.Write(buf); err != nil {
return err
}
return nil
}
func writeVarBytes(w io.Writer, value []byte, numLenBytes int) error {
if err := writeUint(w, uint64(len(value)), numLenBytes); err != nil {
return err
}
if _, err := w.Write(value); err != nil {
return err
}
return nil
}
func readUint(r io.Reader, numBytes int) (uint64, error) {
var l uint64
for i := 0; i < numBytes; i++ {
l <<= 8
var t uint8
if err := binary.Read(r, binary.BigEndian, &t); err != nil {
return 0, err
}
l |= uint64(t)
}
return l, nil
}
// Reads a variable length array of bytes from |r|. |numLenBytes| specifies the
// number of (BigEndian) prefix-bytes which contain the length of the actual
// array data bytes that follow.
// Allocates an array to hold the contents and returns a slice view into it if
// the read was successful, or an error otherwise.
func readVarBytes(r io.Reader, numLenBytes int) ([]byte, error) {
switch {
case numLenBytes > 8:
return nil, fmt.Errorf("numLenBytes too large (%d)", numLenBytes)
case numLenBytes == 0:
return nil, errors.New("numLenBytes should be > 0")
}
l, err := readUint(r, numLenBytes)
if err != nil {
return nil, err
}
data := make([]byte, l)
if n, err := io.ReadFull(r, data); err != nil {
if err == io.EOF || err == io.ErrUnexpectedEOF {
return nil, fmt.Errorf("short read: expected %d but got %d", l, n)
}
return nil, err
}
return data, nil
}
// UnmarshalDigitallySigned reconstructs a DigitallySigned structure from a Reader
func UnmarshalDigitallySigned(r io.Reader) (*DigitallySigned, error) {
var h byte
if err := binary.Read(r, binary.BigEndian, &h); err != nil {
return nil, fmt.Errorf("failed to read HashAlgorithm: %v", err)
}
var s byte
if err := binary.Read(r, binary.BigEndian, &s); err != nil {
return nil, fmt.Errorf("failed to read SignatureAlgorithm: %v", err)
}
sig, err := readVarBytes(r, SignatureLengthBytes)
if err != nil {
return nil, fmt.Errorf("failed to read Signature bytes: %v", err)
}
return &DigitallySigned{
HashAlgorithm: HashAlgorithm(h),
SignatureAlgorithm: SignatureAlgorithm(s),
Signature: sig,
}, nil
}
func marshalDigitallySignedHere(ds DigitallySigned, here []byte) ([]byte, error) {
sigLen := len(ds.Signature)
dsOutLen := 2 + SignatureLengthBytes + sigLen
if here == nil {
here = make([]byte, dsOutLen)
}
if len(here) < dsOutLen {
return nil, ErrNotEnoughBuffer
}
here = here[0:dsOutLen]
here[0] = byte(ds.HashAlgorithm)
here[1] = byte(ds.SignatureAlgorithm)
binary.BigEndian.PutUint16(here[2:4], uint16(sigLen))
copy(here[4:], ds.Signature)
return here, nil
}
// MarshalDigitallySigned marshalls a DigitallySigned structure into a byte array
func MarshalDigitallySigned(ds DigitallySigned) ([]byte, error) {
return marshalDigitallySignedHere(ds, nil)
}
func deserializeSCTV1(r io.Reader, sct *SignedCertificateTimestamp) error {
if err := binary.Read(r, binary.BigEndian, &sct.LogID); err != nil {
return err
}
if err := binary.Read(r, binary.BigEndian, &sct.Timestamp); err != nil {
return err
}
ext, err := readVarBytes(r, ExtensionsLengthBytes)
if err != nil {
return err
}
sct.Extensions = ext
ds, err := UnmarshalDigitallySigned(r)
if err != nil {
return err
}
sct.Signature = *ds
return nil
}
func DeserializeSCT(r io.Reader) (*SignedCertificateTimestamp, error) {
var sct SignedCertificateTimestamp
if err := binary.Read(r, binary.BigEndian, &sct.SCTVersion); err != nil {
return nil, err
}
switch sct.SCTVersion {
case V1:
return &sct, deserializeSCTV1(r, &sct)
default:
return nil, fmt.Errorf("unknown SCT version %d", sct.SCTVersion)
}
}
|
