Struct Trailer 

pub struct Trailer {
    pub checksum: Option<String>,
    pub test_and_training: Option<bool>,
    pub possible_duplicate_emission: Option<PossibleDuplicateEmission>,
    pub delayed_message: Option<bool>,
    pub message_reference: Option<MessageReference>,
    pub possible_duplicate_message: Option<PossibleDuplicateMessage>,
    pub system_originated_message: Option<SystemOriginatedMessage>,
    pub mac: Option<String>,
}

Trailer (Block 5): Message Security and Control Information

Purpose

The Trailer block provides essential security, authentication, and control information for SWIFT messages. It ensures message integrity through checksums, enables duplicate detection, supports message authentication, and provides system-level control information critical for secure and reliable message delivery.

Format Specification

• Block Format: {5:{tag:value}{tag:value}...}
• Tag Types: Three-letter tags with optional values
• Security Tags: MAC and CHK for authentication
• Control Tags: Various operational controls

Business Context Applications

• Message Integrity: Checksum validation for data integrity
• Security Authentication: MAC for message authentication
• Duplicate Detection: Prevention of duplicate processing
• Operational Control: Test messages and system controls

Security and Authentication Tags

CHK: Checksum (Mandatory)

• Format: 12 hexadecimal characters
• Calculation: Algorithm-based on message content
• Purpose: Detect transmission errors
• Validation: Automatic by SWIFT network
• Failure Action: Message rejection

MAC: Message Authentication Code

• Format: Variable length hexadecimal
• Algorithm: Agreed between parties
• Purpose: Authenticate message origin
• Usage: High-value or sensitive messages
• Bilateral: Requires key exchange

Duplicate Control Tags

PDM: Possible Duplicate Message

• Format: Optional time + MOR
• Purpose: Warn of possible duplicate
• Action: Receiver should check for duplicates
• Components: Time (HHMM) + Message Output Reference

PDE: Possible Duplicate Emission

• Format: Optional time + MIR
• Purpose: Sender suspects duplicate sent
• Usage: Network recovery scenarios
• Components: Time (HHMM) + Message Input Reference

Operational Control Tags

TNG: Test and Training

• Format: Empty tag (presence only)
• Purpose: Identifies test messages
• Processing: Should not affect production
• Usage: Testing and training environments
• Warning: Must not be processed as live

DLM: Delayed Message

• Format: Empty tag (presence only)
• Purpose: Indicates delayed transmission
• Cause: Network issues or recovery
• Action: Check value dates and cut-offs

Reference and Tracking Tags

MRF: Message Reference

• Format: Date + Time + MIR
• Purpose: Reference related messages
• Usage: Corrections and cancellations
• Components: YYMMDD + HHMM + full MIR

SYS: System Originated Message

• Format: Optional time + MIR
• Purpose: System-generated messages
• Examples: Automatic responses
• Processing: May have special handling

Message Reference Structures

Message Input Reference (MIR)

• Date: YYMMDD format
• LT Identifier: 12-character sending LT
• Session: 4-digit session number
• Sequence: 6-digit sequence number
• Usage: Unique message identification

Message Output Reference (MOR)

• Format: Same structure as MIR
• Perspective: Receiver’s reference
• Purpose: Delivery confirmation
• Tracking: End-to-end message tracking

Network Validation Requirements

• CHK Mandatory: All messages must have checksum
• Tag Order: Specific ordering requirements
• Format Compliance: Exact format specifications
• Value Validation: Tag-specific validations

Security Considerations

Checksum Protection

• Coverage: Entire message content
• Algorithm: SWIFT-specified calculation
• Tampering: Detects any modification
• Reliability: Very low false positive rate

MAC Authentication

• Bilateral Agreement: Key management required
• Algorithm Choice: Per agreement
• Non-repudiation: Proves message origin
• Legal Standing: Admissible evidence

Duplicate Detection Mechanisms

System Design

• Detection Window: Configurable timeframe
• Reference Tracking: MIR/MOR correlation
• Recovery Support: Post-incident reconciliation
• Audit Trail: Complete duplicate history

Processing Rules

• PDM Messages: Manual review recommended
• Duplicate Window: Typically 24-48 hours
• Action Required: Verify before processing
• Documentation: Record resolution actions

Operational Guidelines

Test Message Handling

• TNG Identification: Clear test marking
• Environment Separation: Test vs production
• Processing Prevention: Automatic filtering
• Audit Exclusion: Separate test reporting

Delayed Message Processing

• DLM Recognition: Special handling required
• Value Date Check: Verify still valid
• Cut-off Impact: May miss deadlines
• Notification: Alert relevant parties

Error Prevention Guidelines

• CHK Calculation: Automatic by system
• Tag Formatting: Follow exact specifications
• Reference Accuracy: Verify MIR/MOR format
• Test Separation: Clear test identification

Integration with Other Blocks

• Block 1-4: Content for checksum calculation
• Block 1: Session/sequence for references
• Block 2: Message type affects trailer options
• Block 3: Some services require specific tags

Compliance Framework

• Security Standards: Cryptographic requirements
• Audit Requirements: Trailer preservation
• Legal Admissibility: Authentication standards
• Regulatory Compliance: Security controls

Recovery and Reconciliation

Message Recovery

• Reference Tracking: Via MIR/MOR
• Duplicate Resolution: PDM/PDE handling
• Audit Support: Complete tag history
• Dispute Resolution: Authentication proof

System Recovery

• Checkpoint References: Recovery points
• Sequence Verification: Gap detection
• Duplicate Prevention: During recovery
• Integrity Validation: CHK verification

Best Practices

• Security First: Always validate CHK
• MAC Usage: For high-value messages
• Duplicate Vigilance: Check PDM warnings
• Test Clarity: Clearly mark test messages

See Also

• SWIFT FIN Security Guide: Authentication Standards
• Checksum Algorithms: Technical Specifications
• Duplicate Detection: Best Practices Guide
• MAC Implementation: Bilateral Agreement Templates

Fields

checksum: Option<String>

CHK - Checksum (12!h) - Mandatory

test_and_training: Option<bool>

TNG - Test & Training Message - Optional (empty tag)

possible_duplicate_emission: Option<PossibleDuplicateEmission>

PDE - Possible Duplicate Emission - Optional

delayed_message: Option<bool>

DLM - Delayed Message - Optional (empty tag)

message_reference: Option<MessageReference>

MRF - Message Reference - Optional

possible_duplicate_message: Option<PossibleDuplicateMessage>

PDM - Possible Duplicate Message - Optional

system_originated_message: Option<SystemOriginatedMessage>

SYS - System Originated Message - Optional

mac: Option<String>

MAC - Message Authentication Code - Optional

Implementations

impl Trailer

pub fn parse(block5: &str) -> Result<Self>

Parse trailer from block 5 string using structured parsing

Trait Implementations

impl Clone for Trailer

fn clone(&self) -> Trailer

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Trailer

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Trailer

fn default() -> Trailer

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Trailer

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Display for Trailer

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl PartialEq for Trailer

fn eq(&self, other: &Trailer) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Trailer

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl StructuralPartialEq for Trailer