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105 lines
2.7 KiB
105 lines
2.7 KiB
8 years ago
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package packet
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import (
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"bytes"
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"io"
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"math/big"
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"github.com/keybase/go-crypto/openpgp/ecdh"
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"github.com/keybase/go-crypto/openpgp/errors"
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"github.com/keybase/go-crypto/openpgp/s2k"
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)
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// ECDHKdfParams generates KDF parameters sequence for given
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// PublicKey. See https://tools.ietf.org/html/rfc6637#section-8
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func ECDHKdfParams(pub *PublicKey) []byte {
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buf := new(bytes.Buffer)
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oid := pub.ec.oid
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buf.WriteByte(byte(len(oid)))
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buf.Write(oid)
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buf.WriteByte(18) // ECDH TYPE
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pub.ecdh.serialize(buf)
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buf.WriteString("Anonymous Sender ")
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buf.Write(pub.Fingerprint[:])
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return buf.Bytes()
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}
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func decryptKeyECDH(priv *PrivateKey, X, Y *big.Int, C []byte) (out []byte, err error) {
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ecdhpriv, ok := priv.PrivateKey.(*ecdh.PrivateKey)
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if !ok {
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return nil, errors.InvalidArgumentError("bad internal ECDH key")
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}
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Sx := ecdhpriv.DecryptShared(X, Y)
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kdfParams := ECDHKdfParams(&priv.PublicKey)
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hash, ok := s2k.HashIdToHash(byte(priv.ecdh.KdfHash))
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if !ok {
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return nil, errors.InvalidArgumentError("invalid hash id in private key")
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}
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key := ecdhpriv.KDF(Sx, kdfParams, hash)
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keySize := CipherFunction(priv.ecdh.KdfAlgo).KeySize()
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decrypted, err := ecdh.AESKeyUnwrap(key[:keySize], C)
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if err != nil {
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return nil, err
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}
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// We have to "read ahead" to discover real length of the
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// encryption key and properly unpad buffer.
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cipherFunc := CipherFunction(decrypted[0])
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// +3 bytes = 1-byte cipher id and checksum 2-byte checksum.
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out = ecdh.UnpadBuffer(decrypted, cipherFunc.KeySize()+3)
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if out == nil {
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return nil, errors.InvalidArgumentError("invalid padding while ECDH")
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}
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return out, nil
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}
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func serializeEncryptedKeyECDH(w io.Writer, rand io.Reader, header [10]byte, pub *PublicKey, keyBlock []byte) error {
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ecdhpub := pub.PublicKey.(*ecdh.PublicKey)
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kdfParams := ECDHKdfParams(pub)
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hash, ok := s2k.HashIdToHash(byte(pub.ecdh.KdfHash))
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if !ok {
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return errors.InvalidArgumentError("invalid hash id in private key")
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}
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kdfKeySize := CipherFunction(pub.ecdh.KdfAlgo).KeySize()
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Vx, Vy, C, err := ecdhpub.Encrypt(rand, kdfParams, keyBlock, hash, kdfKeySize)
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if err != nil {
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return err
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}
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mpis, mpiBitLen := ecdh.Marshal(ecdhpub.Curve, Vx, Vy)
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packetLen := len(header) /* header length in bytes */
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packetLen += 2 /* mpi length in bits */ + len(mpis)
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packetLen += 1 /* ciphertext size in bytes */ + len(C)
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err = serializeHeader(w, packetTypeEncryptedKey, packetLen)
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if err != nil {
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return err
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}
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_, err = w.Write(header[:])
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if err != nil {
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return err
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}
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_, err = w.Write([]byte{byte(mpiBitLen >> 8), byte(mpiBitLen)})
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if err != nil {
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return err
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}
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_, err = w.Write(mpis[:])
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if err != nil {
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return err
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}
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w.Write([]byte{byte(len(C))})
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w.Write(C[:])
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return nil
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}
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