AS2 also known as Applicability Statement 2 is a secure file transfer protocol that enables secure and reliable exchange of electronic data, between organizations over the internet
10 May 2023 by Lahiru Ananda
What is AS2?
AS2 also known as Applicability Statement 2 is a secure file transfer protocol that enables secure and reliable exchange of electronic data, between organizations over the internet. It is widely used in electronic data interchange (EDI) transactions and provides features such as encrypted data transfer, message signing, and receipt acknowledgment. The AS2 protocol helps ensure the confidentiality and integrity of data being transmitted, making it a secure and reliable method for exchanging business-critical information.
The AS2 protocol was introduced in the early 2000s. It was developed as a secure and reliable alternative to traditional file transfer protocols such as FTP (File Transfer Protocol). Since its introduction, AS2 has been widely adopted and has become a standard for secure and reliable EDI transactions. It is supported by many EDI software and service providers, as well as by various industry standards organizations, making it easier for organizations to exchange electronic data in a secure and reliable manner.
Why do we need to use AS2?
As mentioned previously, the AS2 protocol provides a secure and reliable way to exchange electronic data between organizations over the internet. Here are some of the key benefits of using AS2 protocol:
Security: AS2 provides encryption of data in transit and message signing to ensure the confidentiality and integrity of the data being transmitted.
Reliability: AS2 includes a receipt and acknowledgement mechanism, which ensures that both parties know when a message has been successfully received.
Compliance: AS2 is often required by businesses for compliance with various regulations and industry standards, particularly in the context of EDI transactions. It is specifically designed to meet the requirements of the Health Insurance Portability and Accountability Act (HIPAA) in the United States.
Efficiency: AS2 enables batch processing of large data transfers, reducing the amount of manual intervention required and improving the speed and efficiency of data exchange.
In summary, AS2 provides organizations with a secure and reliable way to exchange electronic data over the internet, and is widely used for EDI transactions. The choice of AS2 versus other protocols depends on the specific requirements of the organization and the type of data being transferred.
How does the AS2 protocol work?
AS2 protocol works by using digital certificates, secure communication channels, and encryption algorithms to reliably and securely exchange electronic data between two systems over the internet. The following is a high-level overview of how AS2 works:
Encryption: Before the data is transmitted, it is encrypted to ensure the confidentiality of the data. AS2 supports various encryption algorithms, including AES (Advanced Encryption Standard).
Message signing: A digital signature is generated for the data to ensure the integrity of the message. The digital signature is created using a private key and verified using a public key, which is obtained from the recipient’s X.509 certificate.
Transmission: The encrypted and signed message is transmitted from the sender to the recipient using the HTTP or HTTPS protocols. This allows the message to be transmitted over the internet in a secure and reliable manner.
Receipt and Acknowledgement: Once the recipient has received the message, it generates an acknowledgement (MDN) which is sent back to the sender to confirm that the message was successfully received.
Decryption: Upon receipt of the MDN, the sender decrypts the message and verifies the digital signature to ensure that the data has not been altered in transit.
Encryption in AS2
In the AS2 protocol, encryption is used to protect the payload (the data being exchanged) and the message header (information about the data being exchanged). The encryption process in AS2 is usually done using public key cryptography, which involves the use of a pair of keys: a public key and a private key.
Public key: The Recipient’s public key is used to encrypt the data. The public key is made available to anyone who wants to send data to the recipient.
Private key: The Recipient’s private key is used to decrypt the data encrypted using the public key. The private key is kept secret and only known to the recipient.
When a sender wants to send data to a recipient using AS2, they first encrypt the data using the recipient’s public key. This ensures that only the recipient, who has the corresponding private key, can decrypt the data. The encrypted data is then packaged in an AS2 message and sent over the Internet to the recipient.
Upon receiving the AS2 message, the recipient uses their private key to decrypt the data. This ensures that the data remains secure and confidential during transmission, and can only be accessed by the intended recipient.
Digital Signature in AS2
Digital signatures play an important role in ensuring the authenticity and integrity of data transmitted through the AS2 protocol. When a sender sends data to a recipient using AS2, they use a digital signature to prove that the data has not been tampered with during transmission and that the sender is who they say they are.
Like in the encryption, generating a digital signature process also involves the use of a pair of keys. The difference is this time we use the sender’s private key and public key to generate and verify the digital signature.
A digital signature is created using a mathematical algorithm (hash function) that generates a unique code, called a hash value, that represents the data being signed. A hash function is a mathematical function that converts an input of arbitrary length (in this case message payload) into a fixed-length output (hash value). AS2 protocol commonly uses SHA-1, SHA-256, or SHA-512 hashing algorithms to generate the hash codes.
Once generated the hash value for the payload, it is then encrypted using the sender’s private key. creating a digital signature that can be attached to the message. This creates a digital signature that is unique to the data being sent and the sender’s private key.
When the recipient receives the AS2 message, it extracts the digital signature and the encrypted data. They then decrypt the digital signature using the sender’s public key, which is made available to anyone who wants to verify the signature.
The recipient then creates a new hash of the decrypted data using the same hash algorithm as the sender. If the newly created hash matches the decrypted hash in the digital signature, this indicates that the data has not been tampered with during transmission and that the signature is valid. This provides the recipient with the assurance that the data they have received is authentic and has not been tampered with during transit.
If the newly created hash does not match the decrypted hash in the digital signature, this indicates that the data has been tampered with or corrupted during transmission, and the signature is invalid. In this case, the recipient can reject the data or request its forwarding.
MDN in AS2
Message Disposition Notification (MDN), is a key component of the AS2 protocol which provides feedback to the sender regarding the status of the transmission and whether the recipient has successfully received and processed the data.
When a sender sends a message using AS2, they can request an MDN from the recipient. The MDN can be sent either synchronously, in which case the MDN is sent back immediately after the message has been received and processed over the same connection that was used to transmit the original message. Alternatively, Sender can request the MDN asynchronously, in which case the MDN is sent back at a later time over a separate HTTP connection.
The MDN message contains information about the disposition of the message, such as whether it was successfully received and processed, or whether an error occurred during transmission.
The disposition of the message can be one of the following:
processed - this indicates that the message was successfully received and processed by the recipient’s system.
processed with warning - this indicates that the message was received and processed by the recipient’s system, but with some warnings or errors.
failed - this indicates that the message could not be processed by the recipient’s system due to errors or other issues.
The MDN also contains information about the original message, such as the message ID and any other information that was included in the original message header.
Are there similar protocols to AS2?
The AS4 (Applicability Statement 4) protocol was introduced in early 2010s, as a more advanced and improved version of the AS2 protocol. AS4 was designed to meet the needs of modern businesses and organizations, who require more advanced security and reliability features for exchanging electronic data over the internet. The protocol is widely supported by EDI software and service providers, and is becoming increasingly popular for secure and reliable EDI transactions.
If AS4 is more secure and reliable, why do people most often use AS2 instead of AS4?
AS2 is more widely adopted and has been around for longer, which is why it is still more commonly used than AS4. Additionally, AS2 provides sufficient security and reliability for many organizations and their use cases, and upgrading to AS4 may not be necessary.
Another factor to consider is that AS4 is a newer protocol and may not be as widely supported as AS2 by various systems and tools. Upgrading to AS4 may require investment in new software or systems, which can be a barrier for some organizations.
Finally, the choice between AS2 and AS4 also depends on the specific requirements of the organization and the type of data being transferred. For organizations that require more advanced security and reliability features, AS4 may be a better choice, but for many organizations, AS2 provides sufficient security and reliability for their needs.
In conclusion, while AS4 may offer enhanced security and reliability features, many organizations still choose to use AS2 due to its wider adoption, lower costs, and sufficient security and reliability for their needs.
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