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73 lines
2.5 KiB
Go
73 lines
2.5 KiB
Go
// Package ciphersuite provides the crypto operations needed for a DTLS CipherSuite
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package ciphersuite
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import (
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"encoding/binary"
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"errors"
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"github.com/pion/dtls/v2/pkg/protocol"
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"github.com/pion/dtls/v2/pkg/protocol/recordlayer"
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)
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var (
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errNotEnoughRoomForNonce = &protocol.InternalError{Err: errors.New("buffer not long enough to contain nonce")} //nolint:goerr113
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errDecryptPacket = &protocol.TemporaryError{Err: errors.New("failed to decrypt packet")} //nolint:goerr113
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errInvalidMAC = &protocol.TemporaryError{Err: errors.New("invalid mac")} //nolint:goerr113
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)
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func generateAEADAdditionalData(h *recordlayer.Header, payloadLen int) []byte {
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var additionalData [13]byte
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// SequenceNumber MUST be set first
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// we only want uint48, clobbering an extra 2 (using uint64, Golang doesn't have uint48)
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binary.BigEndian.PutUint64(additionalData[:], h.SequenceNumber)
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binary.BigEndian.PutUint16(additionalData[:], h.Epoch)
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additionalData[8] = byte(h.ContentType)
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additionalData[9] = h.Version.Major
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additionalData[10] = h.Version.Minor
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binary.BigEndian.PutUint16(additionalData[len(additionalData)-2:], uint16(payloadLen))
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return additionalData[:]
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}
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// examinePadding returns, in constant time, the length of the padding to remove
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// from the end of payload. It also returns a byte which is equal to 255 if the
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// padding was valid and 0 otherwise. See RFC 2246, Section 6.2.3.2.
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//
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// https://github.com/golang/go/blob/039c2081d1178f90a8fa2f4e6958693129f8de33/src/crypto/tls/conn.go#L245
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func examinePadding(payload []byte) (toRemove int, good byte) {
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if len(payload) < 1 {
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return 0, 0
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}
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paddingLen := payload[len(payload)-1]
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t := uint(len(payload)-1) - uint(paddingLen)
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// if len(payload) >= (paddingLen - 1) then the MSB of t is zero
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good = byte(int32(^t) >> 31)
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// The maximum possible padding length plus the actual length field
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toCheck := 256
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// The length of the padded data is public, so we can use an if here
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if toCheck > len(payload) {
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toCheck = len(payload)
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}
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for i := 0; i < toCheck; i++ {
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t := uint(paddingLen) - uint(i)
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// if i <= paddingLen then the MSB of t is zero
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mask := byte(int32(^t) >> 31)
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b := payload[len(payload)-1-i]
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good &^= mask&paddingLen ^ mask&b
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}
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// We AND together the bits of good and replicate the result across
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// all the bits.
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good &= good << 4
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good &= good << 2
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good &= good << 1
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good = uint8(int8(good) >> 7)
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toRemove = int(paddingLen) + 1
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return toRemove, good
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}
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