067a4c38f8
signedData was ambiguous — it did not convey that the buffer holds accumulated header TLVs fed as input to HMAC, nor whether data was already signed or pending signing. hmacInputBuffer makes the purpose unambiguous on first read (AX Principle 1: predictable names over short names). Co-Authored-By: Charon <charon@lethean.io>
111 lines
3 KiB
Go
111 lines
3 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 = packetError("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 = packetError("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
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Payload []byte
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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 == 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 hmacInputBuffer bytes.Buffer
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header := UEPSHeader{}
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var hmacSignature []byte
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var payload []byte
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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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tagValueLength, 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, tagValueLength)
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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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header.Version = tagValue[0]
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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hmacInputBuffer.Write(tagValue)
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case TagCurrentLayer:
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header.CurrentLayer = tagValue[0]
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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hmacInputBuffer.Write(tagValue)
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case TagTargetLayer:
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header.TargetLayer = tagValue[0]
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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hmacInputBuffer.Write(tagValue)
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case TagIntent:
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header.IntentID = tagValue[0]
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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hmacInputBuffer.Write(tagValue)
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case TagThreatScore:
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header.ThreatScore = binary.BigEndian.Uint16(tagValue)
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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hmacInputBuffer.Write(tagValue)
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case TagHMAC:
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hmacSignature = tagValue
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default:
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// hmacInputBuffer.Write([]byte{tagType, tagValueLength}); hmacInputBuffer.Write(tagValue) — unknown tags included in HMAC
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hmacInputBuffer.WriteByte(tagType)
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hmacInputBuffer.WriteByte(tagValueLength)
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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: header,
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Payload: payload,
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}, nil
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}
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