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What's the Difference Between AS2, AS3, and AS4

AS2, AS3, and AS4: What is the Distinction?

If you think these three protocols are simply sequential updates from the 1990s’ AS1 protocol you’d be mistaken. Each protocol brings its own distinct features to the data transmission table. Here’s a few key differences between them.

What is AS2?

AS2 (Applicability Statement 2) is a protocol specification used to transmit sensitive data securely and reliably over the internet. AS2 supports the encryption of messages between trading partners and vendors via HTTPS. Data is protected with digital certificates and encryption standards while in transit across systems, networks, and locations.

Why Use AS2?

Organizations often choose AS2 over other file transfer protocols (like FTP or SFTP) because of how easily the protocol helps them meet regulatory compliance requirements and trading partner needs. AS2 serves as a standard used to transfer EDI or other data. Advantages include:

  • End-to-end encryption
  • Ability to send/retrieve file transfers of any size or volume
  • Digital signature authentication for senders and receivers
  • MDN (Message Disposition Notification) alerts to verify messages were successfully received and decrypted
  • Validation of file integrity with confirmation of successful transfers

Related Reading: Which is Better: AS2 vs. SFTP?

What is AS3?

With the AS3 specification, applications communicate EDI data or other information using the FTP protocol. It’s not, however, just the latest and greatest edition of AS2. Rather, AS3 provides a layer of security for data transmission through digital signatures and data encryption.

Why Use AS3?

This specification offers flexibility, security and non-repudiation receipt (NPR), which gives the sender legal proof of unaltered delivery and verification that the message received is identical to what was sent. Other benefits include:

  • End-to-end data encryption
  • SSL encryption and hashing
  • Confirmation of receipts or MDNs
  • Proof of transaction details
  • Large file transfer capabilities
  • Ability to send any data type

What is AS4?

AS4, the latest option superseding AS2, is an open business-to-business (B2B) standard for securing and exchanging documents between businesses using web services.

Why Use AS4?

AS4 is frequently used for EDI integration projects. Other advantages include:

  • Used for both client and server (push and pull actions)
  • Receipts delivered as SOAP (Simple Object Access Protocol) messages with XML digital signatures
  • Payload agnostic
  • Combines MIME and SOAP for message packaging (AS2 is purely MIME-based)
  • Security based on WS-Security standard vs. AS2’s S/MIME specifications

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