Methods and apparatuses for selective data encryption

1. A method of encryption of a message M of uniformly distributed symbols using an encryption key K with key length k, the method being performed using a processor in an encryption device and comprising the steps of:

determining if the message M is longer than, as long as, or shorter than the key length k; and

encrypting the message M;

wherein k bits are encrypted for the message M with a length of k bits;

wherein exactly k bits are encrypted for the message M with a length longer than k bits; and

for a message M with a length shorter than the key length k:

concatenating the message M with at least one further message in order to obtain a lengthened message at least k bits long; and

encrypting exactly k bits of the lengthened message.

2. The method of claim 1 , wherein the uniformly distributed symbols further are causal.

3. The method of claim 1 , wherein the at least one message M is JPEG2000 encoded.

4. An apparatus for encryption of at least one message M of uniformly distributed symbols using an encryption key K with key length k, the apparatus comprising a processor configured to:

determine if the message M is longer than, as long as, or shorter than the key length k; and

encrypt the message M;

wherein the processor is configured to encrypt k bits of each message M with a length of k bits, encrypt exactly k bits of the message M having a length longer than k bits, and for a message M having a length shorter than the key length k:

concatenate the message M with at least one further message in order to obtain a lengthened message at least k bits long; and

encrypt exactly k bits of the lengthened message.

5. A method of decryption of an encrypted message using a decryption key with key length k, the method being performed using a processor in an decryption device and comprising the steps of:

determining if the encrypted message is longer than, as long as, or short than the key length k;

decrypting each of the at least one encrypted message;

wherein k bits are decrypted for the encrypted message with a length of k bits;

wherein exactly k bits of the encrypted message are decrypted for the encrypted message having a length longer than k bits; and

for the encrypted message having a length shorter than k bits:

concatenating the encrypted message with at least one further encrypted message in order to obtain a lengthened message at least k bits long; and

decrypting exactly k bits of the lengthened message.

6. An apparatus for decryption of at least one encrypted message using a decryption key with key length k, the apparatus comprising a processor configured to:

determine if the encrypted message is longer than, as long as, or shorter than the key length k; and

decrypt the encrypted message;

wherein the processor is configured to decrypt k bits of the encrypted message having a length of k bits;

wherein the processor is configured to decrypt exactly k bits of the encrypted message having a length longer than k bits; and

for the encrypted message having a length shorter than k bits:

concatenate the encrypted message with at least one further encrypted message in order to obtain a lengthened message at least k bits long; and

decrypt exactly k bits of the lengthened message.

7. The method of claim 5 , wherein the encrypted message is at least part of a payload of a packet.

8. The method of claim 5 , wherein the encrypted message comprises encrypted data of a bit stream.

9. The method of claim 8 , wherein the at least one further encrypted message comprises encrypted data of the bit stream and is payload of a further packet.

10. The apparatus of claim 6 , wherein the encrypted message is at least part of a payload packet.

11. The apparatus of claim 6 , wherein the encrypted message comprises encrypted data of a bit stream.

12. The apparatus of claim 11 , wherein the at least one further encrypted message comprises encrypted data of the bit stream and is payload of a further packet.

13. The apparatus of claim 6 , wherein the message comprises entropy encoded data.

14. the apparatus of claim 13 , wherein the entropy encoded data has been coded by a context-based encoder.

15. The apparatus of claim 6 , wherein the encrypted message is an encryption of at least one JPEG encoded codeblock.