Encryption method, decryption method, and related apparatus

1. A method, comprising:

receiving an initial layer-3 message, wherein the initial layer-3 message comprises an indication indicating that a part of the initial layer-3 message is encrypted;

generating a keystream; and

decrypting the encrypted part of the initial layer-3 message by performing an exclusive OR operation on the keystream and the initial layer-3 message.

2. The method according to claim 1 , wherein the encrypted part of the initial layer-3 message comprises small data.

3. The method according to claim 1 , wherein the encrypted part of the initial layer-3 message comprises one or more internet protocol (IP) packets.

4. The method according to claim 1 , wherein the encrypted part of the initial layer-3 message comprises one or more short message service (SMS) messages.

5. The method according to claim 1 , wherein a length of the keystream is equal to a length of the encrypted part of the initial layer-3 message.

6. The method according to claim 5 , wherein generating the keystream comprises generating the keystream by using an evolved packet system encryption algorithm, and wherein the length of the encrypted part of the initial layer-3 message is used as an input parameter of the evolved packet system encryption algorithm.

7. The method according to claim 1 , wherein a length of the keystream is equal to a length of the initial layer-3 message.

8. The method according to claim 7 , wherein generating the keystream comprises:

generating an initial keystream using an evolved packet system encryption algorithm, wherein the length of the initial layer-3 message is an input parameter of the evolved packet system encryption algorithm;

identifying, according to a format of the initial layer-3 message and a length of the encrypted part of the initial layer-3 message, location of the encrypted part in the initial layer-3 message; and

generating the keystream based on a part of the initial keystream that corresponds to the location of the encrypted part in the initial layer-3 message.

9. The method according to claim 8 , wherein generating the keystream based on the part of the initial keystream that corresponds to the location of the encrypted part in the initial layer-3 message comprises:

determining bit positions in the initial keystream that correspond to the encrypted part in the initial layer-3 message;

generating the keystream by keeping bit values at the bit positions in the initial keystream that correspond to the encrypted part in the initial layer-3 message; and

setting bit values at other bit positions in the initial keystream to zero.

10. An apparatus, comprising:

a processor and a storage medium storing program instructions, wherein the instructions, when executed by the processor, enable the apparatus to:

receive an initial layer-3 message, wherein the initial layer-3 message comprises an indication indicating that a part of the initial layer-3 message is encrypted;

generate a keystream; and

decrypt the encrypted part of the initial layer-3 message by performing an exclusive OR operation on the keystream and the initial layer-3 message.

11. The apparatus according to claim 10 , wherein the encrypted part of the initial layer-3 message comprises small data.

12. The apparatus according to claim 10 , wherein the encrypted part of the initial layer-3 message comprises one or more internet protocol (IP) packets.

13. The apparatus according to claim 10 , wherein the encrypted part of the initial layer-3 message comprises one or more short message service (SMS) messages.

14. The apparatus according to claim 10 , wherein a length of the keystream is equal to a length of the encrypted part of the initial layer-3 message.

15. The apparatus according to claim 14 , wherein in generating the keystream, the instructions, when executed by the processor, cause the apparatus to generate the keystream using an evolved packet system encryption algorithm, and wherein the length of the encrypted part of the initial layer-3 message is an input parameter of the evolved packet system encryption algorithm.

16. The apparatus according to claim 10 , wherein a length of the keystream is equal to a length of the initial layer-3 message.

17. The apparatus according to claim 16 , wherein in generating the keystream, the instructions, when executed by the processor, cause the apparatus to:

generate an initial keystream using an evolved packet system encryption algorithm, wherein the length of the initial layer-3 message is an input parameter of the evolved packet system encryption algorithm;

identify, according to a format of the initial layer-3 message and a length of the encrypted part of the initial layer-3 message, location of the encrypted part in the initial layer-3 message;

generate the keystream based on a part of the initial keystream that corresponds to the location of the encrypted part in the initial layer-3 message.

18. The apparatus according to claim 17 , wherein in generating the keystream based on the part of the initial keystream that corresponds to the location of the encrypted part in the initial layer-3 message, the instructions, when executed by the processor, cause the apparatus to:

determine bit positions in the initial keystream that correspond to the encrypted part in the initial layer-3 message;

generate the keystream by keeping bit values at the bit positions in the initial keystream that correspond to the encrypted part in the initial layer-3 message; and

set bit values at other bit positions in the initial keystream to zero.

19. A non-transitory computer-readable storage medium comprising instructions which, when executed by a computer of a communications apparatus, cause the communications apparatus to:

receive an initial layer-3 message, wherein the initial layer-3 message comprises an indication indicating that a part of the initial layer-3 message is encrypted;

generate a keystream; and

decrypt the encrypted part of the initial layer-3 message by performing an exclusive OR operation on the keystream and the initial layer-3 message.

20. The non-transitory computer-readable storage medium according to claim 19 , wherein the encrypted part of the initial layer-3 message comprises small data.