Secure transmission system

• US 20040249817A1
• Filed: 07/01/2004
• Published: 12/09/2004
• Est. Priority Date: 06/28/1999
• Status: Active Grant

• Current Assignee: Zix Corporation (Open Text Corporation)
• Original Assignee: Zix Corporation (Open Text Corporation)
• Inventors: Liu, Gary G., Cook, David P.
• Granted Patent: US 7,493,661 B2
• Time in Patent Office: Days
• US Class Current: 707/9
• CPC Class Codes: H04L 63/0428 wherein the data content is protected, e.g. by encrypting or encapsulating the payload
• CPC Class Codes: H04L 63/0435 wherein the sending and receiving network entities apply symmetric encryption, i.e. same key used for encryption and decryption cryptographic mechanisms or cryptographic arrangements for symmetric key encryption H04L9/06
• CPC Class Codes: H04L 63/061 for key exchange, e.g. in peer-to-peer networks cryptographic mechanisms or cryptographic arrangements for key agreement H04L9/0838
• CPC Class Codes: H04L 63/123 received data contents, e.g. message integrity

Abstract

A method and apparatus for transferring a message securely from a sender to a recipient over a network and includes at each transfer: creating a message; retrieving the public key of the recipient from an external key server just prior to sending the message; signing the message using the private key of the sender; encrypting the signed message using a public key encryption algorithm and the public key of the recipient producing an encrypted signed message; generating an E-mail message addressed to the recipient; attaching the encrypted signed message as an attachment to the E-mail message; and, transmitting the E-mail message to the recipient.

Claims

1. In a public key encryption system that includes a central key repository and a plurality of users, where a user'"'"'s public key is stored at the central key repository and user'"'"'s associated private key is stored locally on a user'"'"'s computer, a method for recovering lost keys, comprising:

designating a recovery question and an answer to the recovery question;

encrypting the user'"'"'s private key using a first hash of the answer as a session key in a symmetric key encryption process;

hashing the answer a predetermined number of times to generate a second hash of the answer;

storing the second hash and the recovery question at the central key repository without exposing the answer to the recovery question to the central key repository;

and when prompted by the user to recover a lost private key;

receiving the answer;

hashing the answer the predetermined number of time to generate a third hash and transmitting the third hash to the central key repository without transmitting the answer itself;

comparing the second and third hashes;

if the second and third hashes match, returning the encrypted private key to the user; and

decrypting the private key using the first hash and storing the private key.

2. The method of claim 1, further comprising:

at a signature manager, hashing the answer to generate the first hash.

3. The method of claim 2, further comprising:

at the signature manager, decrypting the encrypted user'"'"'s private key.

4. The method of claim 1, wherein:

hashing the answer a predetermined number of times to generate a second hash includes adding a constant string to the answer prior to hashing the answer.

5. The method of claim 1, further comprising:

storing the user'"'"'s email address at the central key repository with the second hash and the recovery question.

6. A computer-implemented method for recovering lost data, comprising:

determining a recovery question having an answer to the recovery question;

encrypting data using a first hash of the answer as a symmetric key, wherein the answer has been hashed a first predetermined number of times to generate the first hash of the answer;

hashing the answer a second predetermined number of times to generate a second hash of the answer, wherein the first predetermined number of times differs from the second predetermined number of times;

storing the encrypted data, the second hash and the recovery question at a central repository, wherein the central repository does not receive the answer to the recovery question;

upon receiving a request for the data, providing the recovery question to a user and requesting the answer from the user;

upon the user providing the answer, hashing the provided answer the second predetermined number of times to generate a third hash of the answer;

transmitting the third hash to the central repository without transmitting the provided answer;

comparing the second and third hashes;

if the second and third hashes match, sending the encrypted data to the user; and

decrypting the encrypted data using the symmetric key.

7. The method of claim 6, wherein:

hashing the answer a second predetermined number of times to generate a second hash includes adding a constant string to the answer prior to hashing the answer.

8. The method of claim 6, further comprising:

hashing the answer the first predetermined number of times to generate the first hash of the answer.