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

Three of the most used Secure Transfer Protocols in the world are AS2, AS3 and AS4. If you think these three protocols are simple updates compared to the 1990's AS1 protocol you are greatly mistaken. Want to know which distinct features separates these protocols? Read our blog below.

Three of the most used Secure Transfer Protocols in the world are AS2, AS3 and AS4. If you think these three protocols are simple updates compared to the 1990's AS1 protocol you are greatly mistaken. They all bring their own distinct features to the Data Communication Table and they all have their strengths in a particular area. Here are a few key differences between all three protocols.

What is AS2?

Applicability Statement 2 is a standard used to transfer EDI or other data, such as XML or plain text documents, over the Internet using HTTP and HTTPs. AS2 offers increased verification and security through the use of receipts, digital signatures, and file encryption. Its transactions and acknowledgments occur in real time, increasing the efficiency of document exchanges.

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

What is AS3?

Applicability Statement 3 enables software applications to systematically communicate data, including EDI and XML, over the Internet using file transfer protocol (FTP). AS3 is not the next version of AS2; it offers its own unique features and provides security for the transport payload through digital signatures and data encryption. AS3 may be particularly well-suited for FTP-centric businesses that have a significant investment in FTP scripting, applications, or security.

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?

Applicability Statement 4 was defined in 2013 to be payload agnostic, with specifications based on the functional requirements of AS2. AS4 is an open Business-to-Business (B2B) standard for securing and exchanging documents between businesses using Web Services. The protocol supports compression, SOAP enveloping, encryption, and security tokens, with non-repudiation features similar to those of AS2.

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
  • Is becoming the required protocol in goverment, gas/energy communication and data integration projects


Like we stated before all three protocols have their unique benefits and features and some are required in certain branches above the others. Now that we have stated the differences you might have questions which solution you need for your requirements. Our solutions provide support for exchanging files via AS4 as well as AS3 and AS2. Using MFT with AS4/3/2 consolidates the whole transfer process and allows for single pane of glass administration as well as auditing capabilities.

At ECS we have over 20 years of experience choosing the correct Data Communication/Integration solutions and have done over 1.000 implementations so far. If you have any questions or are in need to implement AS2, AS3 or AS4, contact us for support.