// hashCore hashes a SectionReader using the ImoHash parameters.
func (imo *ImoHash) hashCore(f *io.SectionReader) [Size]byte {
var result [Size]byte
imo.hasher.Reset()
if f.Size() < int64(imo.sampleThreshold) || imo.sampleSize < 1 {
buffer := make([]byte, f.Size())
f.Read(buffer)
imo.hasher.Write(buffer)
} else {
buffer := make([]byte, imo.sampleSize)
f.Read(buffer)
imo.hasher.Write(buffer)
f.Seek(f.Size()/2, 0)
f.Read(buffer)
imo.hasher.Write(buffer)
f.Seek(int64(-imo.sampleSize), 2)
f.Read(buffer)
imo.hasher.Write(buffer)
}
hash := imo.hasher.Sum(nil)
binary.PutUvarint(hash, uint64(f.Size()))
copy(result[:], hash)
return result
}
/*ParsePackHeader A header appears at the beginning and consists of the following:
4-byte signature:
The signature is: {'P', 'A', 'C', 'K'}
4-byte version number (network byte order):
Git currently accepts version number 2 or 3 but
generates version 2 only.
4-byte number of objects contained in the pack (network byte order)
Observation: we cannot have more than 4G versions ;-) and
more than 4G objects in a pack.
*/
func ParsePackHeader(pack *io.SectionReader) (version, objectCount uint32, err error) {
buf := make([]byte, 12)
_, err = pack.Read(buf)
if err != nil {
return
}
if signature := string(buf[:4]); signature != packSignature {
err = errors.New("pack header has wrong signature: " + signature)
return
}
version = binary.BigEndian.Uint32(buf[4:8])
if version != 2 {
err = fmt.Errorf("version unsupport: %d ", version)
return
}
objectCount = binary.BigEndian.Uint32(buf[8:])
return
}
// newDecryptionReader returns an authenticated, decryption reader
func newDecryptionReader(r *io.SectionReader, f *File) (io.Reader, error) {
keyLen := aesKeyLen(f.aesStrength)
saltLen := keyLen / 2 // salt is half of key len
if saltLen == 0 {
return nil, ErrDecryption
}
// grab the salt and pwvv
saltpwvv := make([]byte, saltLen+2)
if _, err := r.Read(saltpwvv); err != nil {
return nil, err
}
salt := saltpwvv[:saltLen]
pwvv := saltpwvv[saltLen : saltLen+2]
// generate keys only if we have a password
if f.password == nil {
return nil, ErrPassword
}
decKey, authKey, pwv := generateKeys(f.password(), salt, keyLen)
if !checkPasswordVerification(pwv, pwvv) {
return nil, ErrPassword
}
dataOff := int64(saltLen + 2)
dataLen := int64(f.CompressedSize64 - uint64(saltLen) - 2 - 10)
// // TODO(alex): Should the compressed sizes be fixed?
// // Not the ideal place to do this.
// f.CompressedSize64 = uint64(dataLen)
// f.CompressedSize = uint32(dataLen)
data := io.NewSectionReader(r, dataOff, dataLen)
authOff := dataOff + dataLen
authcode := io.NewSectionReader(r, authOff, 10)
ar := newAuthReader(authKey, data, authcode, f.DeferAuth)
dr := decryptStream(decKey, ar)
if dr == nil {
return nil, ErrDecryption
}
return dr, nil
}
