89e70a4449
The switch in ReadAndVerify duplicated the same three hmacInputBuffer.WriteByte/Write calls across five cases plus default. Extracted to a single conditional after the switch: all tags except TagHMAC feed the authenticated input buffer. Behaviour is identical; declarative intent is now clear (AX principle 5 — declarative over imperative). Co-Authored-By: Charon <charon@lethean.io>
103 lines
2.9 KiB
Go
103 lines
2.9 KiB
Go
package ueps
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import (
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"bufio"
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"bytes"
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"crypto/hmac"
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"crypto/sha256"
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"encoding/binary"
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"io"
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)
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// packet, err := ReadAndVerify(bufio.NewReader(conn), secret)
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// if err == errMissingHMAC { /* no HMAC tag found in frame */ }
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var errMissingHMAC = sentinelError("UEPS packet missing HMAC signature")
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// packet, err := ReadAndVerify(bufio.NewReader(conn), wrongSecret)
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// if err == errIntegrityViolation { header.ThreatScore += 100; /* reject packet */ }
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var errIntegrityViolation = sentinelError("integrity violation: HMAC mismatch")
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// dispatch(packet.Header.IntentID, packet.Header.ThreatScore, packet.Payload)
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type ParsedPacket struct {
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Header UEPSHeader // packet.Header.Version == 0x09; packet.Header.IntentID == 0x01; packet.Header.ThreatScore == 0
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Payload []byte // packet.Payload == []byte("hello world")
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}
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// packet, err := ueps.ReadAndVerify(bufio.NewReader(conn), []byte("my-shared-secret"))
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// if err == errMissingHMAC { return } // unauthenticated: no HMAC tag in stream
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// if err == errIntegrityViolation { return } // tampered: HMAC mismatch; reject and raise threat score
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// if err == nil { dispatch(packet.Header.IntentID, packet.Header.ThreatScore, packet.Payload) }
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func ReadAndVerify(reader *bufio.Reader, sharedSecret []byte) (*ParsedPacket, error) {
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var (
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hmacInputBuffer bytes.Buffer
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packetHeader UEPSHeader
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hmacSignature []byte
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payload []byte
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)
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for {
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tagType, err := reader.ReadByte()
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if err != nil {
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return nil, err
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}
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if tagType == TagPayload {
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payload, err = io.ReadAll(reader)
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if err != nil {
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return nil, err
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}
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break
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}
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tagLength, err := reader.ReadByte()
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if err != nil {
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return nil, err
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}
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tagValue := make([]byte, int(tagLength))
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if _, err := io.ReadFull(reader, tagValue); err != nil {
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return nil, err
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}
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switch tagType {
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case TagVersion:
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packetHeader.Version = tagValue[0]
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case TagCurrentLayer:
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packetHeader.CurrentLayer = tagValue[0]
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case TagTargetLayer:
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packetHeader.TargetLayer = tagValue[0]
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case TagIntent:
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packetHeader.IntentID = tagValue[0]
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case TagThreatScore:
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packetHeader.ThreatScore = binary.BigEndian.Uint16(tagValue)
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case TagHMAC:
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hmacSignature = tagValue
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}
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// All tags except TagHMAC contribute to the authenticated input;
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// hmacInputBuffer.Write(tagBytes) covers header TLVs and unknown extension tags.
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if tagType != TagHMAC {
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagLength)
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hmacInputBuffer.Write(tagValue)
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}
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}
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if len(hmacSignature) == 0 {
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return nil, errMissingHMAC
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}
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messageAuthCode := hmac.New(sha256.New, sharedSecret)
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messageAuthCode.Write(hmacInputBuffer.Bytes())
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messageAuthCode.Write(payload)
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expectedMessageAuthCode := messageAuthCode.Sum(nil)
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if !hmac.Equal(hmacSignature, expectedMessageAuthCode) {
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return nil, errIntegrityViolation
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}
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return &ParsedPacket{
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Header: packetHeader,
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Payload: payload,
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}, nil
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}
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