Short message encryption
A method and system for securely communicating information via a low bandwidth channel uses encryption that adds comparatively little overhead to the size of the transmission. This method and system efficiently take advantage of the properties of public key cryptography, a shared secret, a traffic key from the shared secret, an abbreviated initialization vector, and an abbreviated whole message signature. The information and the whole message signature are encrypted using the traffic key with a stream cipher.
1. A method for encrypting information carried in a transmission between a source and a destination, the method comprising:
defining a shared secret using a public key for the destination and a private key for the source;
defining a traffic key from the shared secret and a first nonce;
deriving a message authentication code (MAC) at least in part from the information using the traffic key or the private key of the source;
processing the MAC to obtain an abbreviated MAC, wherein the abbreviated MAC has fewer bits than the MAC;
generating an initialization vector based at least in part on a second nonce, wherein the second nonce has fewer bits than the initialization vector;
encrypting the information along with the abbreviated MAC using the traffic key and the initialization vector, the encryption being performed according to a symmetric cipher; and
transmitting the encrypted information, the encrypted abbreviated MAC, and the second nonce in a message from the source to the destination.
2. The method as recited in claim 1 , wherein the shared secret is derived using a Diffie-Hellman Key Agreement algorithm.
3. The method as recited in claim 1 , wherein the shared secret is derived using an elliptical curve cryptography (ECC) variant of Diffie-Hellman Key Agreement algorithm.
4. The method as recited in claim 1 , wherein:
the message further comprises a to_alias field and a from_alias field;
the to_alias is an alias of a true identifier for the destination and is shorter than the true identifier for the destination; and
the from_alias is an alias of a true identifier for the source and is shorter than the true identifier for the source.
5. The method as recited in claim 4 , wherein the initialization vector comprises a concatenation of the to_alias, the from_alias and the second nonce.
6. The method as recited in claim 4 , wherein the MAC is derived from data comprising the information, the to_alias, the from_alias, and the second nonce.
7. The method as recited in claim 1 , wherein the initialization vector is further based on information not contained in the message.
8. The method as recited in claim 1 , wherein the information is encrypted using a traffic key having between 128 bit and 256 bit cryptographic strength.
9. The method as recited in claim 1 , wherein the information is encrypted using an encryption algorithm selected from the National Security Agency (NSA) Suite B family of algorithms.
10. The method as recited in claim 1 , wherein the encrypted abbreviated MAC and the second nonce add six bytes to the size of the message.
11. The method as recited in claim 1 , wherein the shared secret is a number.
12. The method as recited in claim 1 , wherein encrypting the information and the abbreviated MAC is performed without padding the message.
13. The method as recited in claim 12 , wherein the encrypting is performed by use of a block cipher in counter mode.
14. The method as recited in claim 1 , wherein the processing the MAC comprises truncating the MAC to obtain the abbreviated MAC.
15. The method as recited in claim 1 , wherein the processing the MAC comprises:
dividing the MAC into segments; and
calculating an exclusive-or (XOR) of the segments to obtain the abbreviated MAC.
16. The method as recited in claim 1 , wherein the first nonce is data indicative of a current date and/or time.
17. A method of decrypting information carried in a transmission between a source and a destination, the method comprising:
defining a shared secret using a public key for the source and a private key for the destination;
defining a traffic key from the shared secret and a first nonce;
at the destination, receiving the transmission, wherein the transmission includes encrypted information, an encrypted first abbreviated message authentication code (MAC), and a plaintext second nonce;
at the destination, deriving an initialization vector from the second nonce, wherein the second nonce has fewer bits than the initialization vector;
decrypting the information and the first abbreviated MAC using the initialization vector and the traffic key according to a symmetric cipher;
deriving a message authentication code (MAC) at least in part from the decrypted information using the traffic key or the public key of the source;
processing the MAC to obtain a second abbreviated MAC, wherein the first and second abbreviated MACs each have fewer bits than the MAC; and
authenticating the transmission by comparing the first and second abbreviated MACs.
18. The method as recited in claim 17 , wherein the shared secret is derived using an elliptical curve cryptography (ECC) variant of Diffie-Hellman Key Agreement algorithm.
19. The method as recited in claim 17 , wherein:
the message further comprises a to_alias field and a from_alias field;
the to_alias is an alias of a true identifier for the destination and is shorter than the true identifier for the destination; and
the from_alias is an alias of a true identifier for the source and is shorter than the true identifier for the source.
20. The method as recited in claim 17 , wherein the symmetric cipher is performed without padding by use of a block cipher in a counter mode.
21. The method as recited in claim 17 , wherein the public key of the source is received at the destination from a certificate authority (CA), thereby negating a need for the destination to query a certificate revocation list (CRL) of the CA to check whether the public key is valid.
22. The method as recited in claim 17 , wherein the public key of the source is received at the destination from the source.
23. The method as recited in claim 17 , wherein the processing the MAC comprises truncating the MAC to obtain the second abbreviated MAC.
24. The method as recited in claim 17 , wherein the processing the MAC comprises:
dividing the MAC into segments and
calculating an exclusive-or (XOR) of the segments to obtain the second abbreviated MAC.
25. The method as recited in claim 17 , wherein the first nonce is data indicative of a current date and/or time.