1. Technical Field
This invention relates generally to secure and reliable transmission of data. More particularly, the invention relates to computer-implemented techniques for securely and reliably transmitting an electronic document from a sender to a recipient using a secure, central key managing intermediary.
2. Background Art
With the advent of computers and the Internet, an increasing number of documents are being transmitted in electronic format, and it is becoming increasingly important to be able to deliver these documents in a secure and reliable manner. While unsecured email is perhaps one of the most common electronic delivery methods, it typically is neither secure nor particularly reliable. Other approaches to electronic delivery exist which are more successful in attempting to provide either secure or reliable delivery of documents. Two of the more common approaches are secure electronic mail (a.k.a., secure email) and Secure Socket Layer (“SSL”) based deliveries using a Web site for uploading and downloading of deliveries. However, neither of these delivery methods is fully satisfactory with respect to both security and reliability.
Secure email is similar to unsecured email, except that email messages are secured using encryption. In unsecured email, the sender transmits his message to the recipient in an unencrypted state. Thus, if a third party intercepts the message en route to the recipient, the third party will be able to read the message. In secure email, the sender first encrypts the message using a key and then transmits the encrypted message to the recipient. If a third party intercepts this message, it will be unintelligible to the third party since he presumably does not have enough information to decrypt the message (e.g., the third party normally does not have the correct key required to decrypt the message). The recipient, on the other hand, does have the information required to decrypt the message and therefore can read the message when he receives it. By limiting access to the decryption method and keys, the sender can limit who is able to read an encrypted message. By encrypting the message before transmitting, the message is protected during transmission.
However, secure email is delivered from the sender to the recipient using the same architecture and infrastructure as unsecured email and, therefore, suffers from many of the same drawbacks as unsecured email. For example, email delivery services generally lack reliability due to the architecture of the email delivery system. Conventional email servers are designed upon a store-and-forward architecture. An email message may be routed through several email servers on its way from the sender to the recipient, with each server receiving the incoming message, determining the next server on the message's journey, transmitting the message, and possibly leaving behind a copy causing unnecessary and unmanageable audit trails. No single machine is responsible for ensuring that the entire message has been successfully transmitted from the sender to the recipient. In addition, each of the email servers in the chain from sender to recipient is usually owned and operated by a different party. Since no single company or entity owns the entire delivery chain for the email message, no one company or entity can guarantee reliable delivery or integrity of the message. The storing-and-forwarding of email documents through several servers owned by multiple parties means that email messages get lost, delayed, and corrupted. This makes the overall delivery service unreliable or untrackable. Encrypting an email message may provide some protection against unwanted disclosure during transit, but it does not address the reliability issue and does not guarantee that the message will be delivered to the recipient.
An alternate approach to document delivery services utilizes the Secure Socket Layer Protocol for security. In this approach, a Web site uses its digital certificate to authenticate itself to the sender using the SSL protocol. Once the Web site is authenticated, a secure channel is set up between the sender's browser and the Web site, typically by generating a session key to encrypt transmissions between the two. The document is sent from the sender's browser to the Web site via the secure channel. It is stored at the Web site, typically in unencrypted form, awaiting delivery to the recipient. During delivery, the Web site authenticates itself to the recipient's browser and a secure communications channel is then set up between the Web site and the recipient's browser. The document is delivered to the recipient via the secure channel.
The SSL approach suffers from many drawbacks. For example, although the Web site authenticates itself using its digital certificate, neither the sender nor the recipient authenticates himself using a digital certificate. Typically, these systems would at most require the sender and the recipient to authenticate themselves using passwords, which is weak security. In other words, there is no real assurance that either the sender or the recipient actually is who he claims to be. As a result, there is also a lack of non-repudiation, meaning that at a later time, the sender can plausibly deny having sent the document simply by pointing out that there is no strong evidence of who actually sent the document.
Another drawback is that these systems lack end-to-end security, because SSL secures only the channels. The document typically remains in unencrypted form while it is temporarily stored at the Web site. Hence, a third party which attacks the Web site and gains access to the document will be able to read the document. In addition, if the Web site is untrustworthy (or happens to hire an untrustworthy employee), the document will be vulnerable.
There are also SSL-based services that provide optional password encryption of the documents. These systems provide better security, since the document is encrypted at the point of transmission. However, these systems are difficult to use since they require the sender to communicate the password out-of-band to the recipient, a process that is cumbersome and fraught with security risks. Such a system also does not guarantee non-repudiation, since it neither strongly authenticates a user, nor supports digital signatures, nor ensures that only the recipient could open a delivery.
There are also SSL-based services that provide optional encryption of the documents using certificates. These systems provide end-to-end content security, but are extremely difficult to use because of the need for users to manually obtain the keys and exchange keys prior to encryption. Unfortunately, these systems do not integrate key management with encryption and reliable delivery, leaving the complexity of key management entirely to the user. In addition, a system that requires optional use of certificates cannot guarantee non-repudiation. The absence of a digital signature does not represent the absence of a transaction, because the sender could have opted to not use a certificate. Absolute non-repudiation requires mandatory and uniform use of certificates for all transactions in a system.
Both secure email delivery services and SSL-based delivery services suffer from security and/or reliability concerns. Systems that provide SSL with optional document encryption are difficult to use and are non-transparent. Therefore, there is a need for a delivery system which provides integrated key management so that reliable delivery and end-to-end security can be achieved, thus providing some or all of the following benefits: (1) reliable/guaranteed delivery for transactions—a delivery will not be lost; (2) confidentiality for transactions—only the recipient can open a delivery; and (3) non-repudiation for transactions.