chore: make deps, go mod vendor

vendor/github.com/ProtonMail/go-crypto/openpgp/packet/packet_sequence.go

@@ -0,0 +1,222 @@
+package packet
+
+// This file implements the pushdown automata (PDA) from PGPainless (Paul Schaub)
+// to verify pgp packet sequences. See Paul's blogpost for more details:
+// https://blog.jabberhead.tk/2022/10/26/implementing-packet-sequence-validation-using-pushdown-automata/
+import (
+	"fmt"
+
+	"github.com/ProtonMail/go-crypto/openpgp/errors"
+)
+
+func NewErrMalformedMessage(from State, input InputSymbol, stackSymbol StackSymbol) errors.ErrMalformedMessage {
+	return errors.ErrMalformedMessage(fmt.Sprintf("state %d, input symbol %d, stack symbol %d ", from, input, stackSymbol))
+}
+
+// InputSymbol defines the input alphabet of the PDA
+type InputSymbol uint8
+
+const (
+	LDSymbol InputSymbol = iota
+	SigSymbol
+	OPSSymbol
+	CompSymbol
+	ESKSymbol
+	EncSymbol
+	EOSSymbol
+	UnknownSymbol
+)
+
+// StackSymbol defines the stack alphabet of the PDA
+type StackSymbol int8
+
+const (
+	MsgStackSymbol StackSymbol = iota
+	OpsStackSymbol
+	KeyStackSymbol
+	EndStackSymbol
+	EmptyStackSymbol
+)
+
+// State defines the states of the PDA
+type State int8
+
+const (
+	OpenPGPMessage State = iota
+	ESKMessage
+	LiteralMessage
+	CompressedMessage
+	EncryptedMessage
+	ValidMessage
+)
+
+// transition represents a state transition in the PDA
+type transition func(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error)
+
+// SequenceVerifier is a pushdown automata to verify
+// PGP messages packet sequences according to rfc4880.
+type SequenceVerifier struct {
+	stack []StackSymbol
+	state State
+}
+
+// Next performs a state transition with the given input symbol.
+// If the transition fails a ErrMalformedMessage is returned.
+func (sv *SequenceVerifier) Next(input InputSymbol) error {
+	for {
+		stackSymbol := sv.popStack()
+		transitionFunc := getTransition(sv.state)
+		nextState, newStackSymbols, redo, err := transitionFunc(input, stackSymbol)
+		if err != nil {
+			return err
+		}
+		if redo {
+			sv.pushStack(stackSymbol)
+		}
+		for _, newStackSymbol := range newStackSymbols {
+			sv.pushStack(newStackSymbol)
+		}
+		sv.state = nextState
+		if !redo {
+			break
+		}
+	}
+	return nil
+}
+
+// Valid returns true if RDA is in a valid state.
+func (sv *SequenceVerifier) Valid() bool {
+	return sv.state == ValidMessage && len(sv.stack) == 0
+}
+
+func (sv *SequenceVerifier) AssertValid() error {
+	if !sv.Valid() {
+		return errors.ErrMalformedMessage("invalid message")
+	}
+	return nil
+}
+
+func NewSequenceVerifier() *SequenceVerifier {
+	return &SequenceVerifier{
+		stack: []StackSymbol{EndStackSymbol, MsgStackSymbol},
+		state: OpenPGPMessage,
+	}
+}
+
+func (sv *SequenceVerifier) popStack() StackSymbol {
+	if len(sv.stack) == 0 {
+		return EmptyStackSymbol
+	}
+	elemIndex := len(sv.stack) - 1
+	stackSymbol := sv.stack[elemIndex]
+	sv.stack = sv.stack[:elemIndex]
+	return stackSymbol
+}
+
+func (sv *SequenceVerifier) pushStack(stackSymbol StackSymbol) {
+	sv.stack = append(sv.stack, stackSymbol)
+}
+
+func getTransition(from State) transition {
+	switch from {
+	case OpenPGPMessage:
+		return fromOpenPGPMessage
+	case LiteralMessage:
+		return fromLiteralMessage
+	case CompressedMessage:
+		return fromCompressedMessage
+	case EncryptedMessage:
+		return fromEncryptedMessage
+	case ESKMessage:
+		return fromESKMessage
+	case ValidMessage:
+		return fromValidMessage
+	}
+	return nil
+}
+
+// fromOpenPGPMessage is the transition for the state OpenPGPMessage.
+func fromOpenPGPMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	if stackSymbol != MsgStackSymbol {
+		return 0, nil, false, NewErrMalformedMessage(OpenPGPMessage, input, stackSymbol)
+	}
+	switch input {
+	case LDSymbol:
+		return LiteralMessage, nil, false, nil
+	case SigSymbol:
+		return OpenPGPMessage, []StackSymbol{MsgStackSymbol}, false, nil
+	case OPSSymbol:
+		return OpenPGPMessage, []StackSymbol{OpsStackSymbol, MsgStackSymbol}, false, nil
+	case CompSymbol:
+		return CompressedMessage, nil, false, nil
+	case ESKSymbol:
+		return ESKMessage, []StackSymbol{KeyStackSymbol}, false, nil
+	case EncSymbol:
+		return EncryptedMessage, nil, false, nil
+	}
+	return 0, nil, false, NewErrMalformedMessage(OpenPGPMessage, input, stackSymbol)
+}
+
+// fromESKMessage is the transition for the state ESKMessage.
+func fromESKMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	if stackSymbol != KeyStackSymbol {
+		return 0, nil, false, NewErrMalformedMessage(ESKMessage, input, stackSymbol)
+	}
+	switch input {
+	case ESKSymbol:
+		return ESKMessage, []StackSymbol{KeyStackSymbol}, false, nil
+	case EncSymbol:
+		return EncryptedMessage, nil, false, nil
+	}
+	return 0, nil, false, NewErrMalformedMessage(ESKMessage, input, stackSymbol)
+}
+
+// fromLiteralMessage is the transition for the state LiteralMessage.
+func fromLiteralMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	switch input {
+	case SigSymbol:
+		if stackSymbol == OpsStackSymbol {
+			return LiteralMessage, nil, false, nil
+		}
+	case EOSSymbol:
+		if stackSymbol == EndStackSymbol {
+			return ValidMessage, nil, false, nil
+		}
+	}
+	return 0, nil, false, NewErrMalformedMessage(LiteralMessage, input, stackSymbol)
+}
+
+// fromLiteralMessage is the transition for the state CompressedMessage.
+func fromCompressedMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	switch input {
+	case SigSymbol:
+		if stackSymbol == OpsStackSymbol {
+			return CompressedMessage, nil, false, nil
+		}
+	case EOSSymbol:
+		if stackSymbol == EndStackSymbol {
+			return ValidMessage, nil, false, nil
+		}
+	}
+	return OpenPGPMessage, []StackSymbol{MsgStackSymbol}, true, nil
+}
+
+// fromEncryptedMessage is the transition for the state EncryptedMessage.
+func fromEncryptedMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	switch input {
+	case SigSymbol:
+		if stackSymbol == OpsStackSymbol {
+			return EncryptedMessage, nil, false, nil
+		}
+	case EOSSymbol:
+		if stackSymbol == EndStackSymbol {
+			return ValidMessage, nil, false, nil
+		}
+	}
+	return OpenPGPMessage, []StackSymbol{MsgStackSymbol}, true, nil
+}
+
+// fromValidMessage is the transition for the state ValidMessage.
+func fromValidMessage(input InputSymbol, stackSymbol StackSymbol) (State, []StackSymbol, bool, error) {
+	return 0, nil, false, NewErrMalformedMessage(ValidMessage, input, stackSymbol)
+}