RC5, introduced by R.Rivest, is a fast symmetric block cipher that has a variable block size, variable key length, variable number of rounds and heavily uses data-independent rotations. Intel IPP for Cryptography implements functions for RC5 algorithm with 64- and 128-bit block sizes.
This section describes functions for various operational modes of RC5 cipher systems. The functions are implemented to comply with the RC5 cipher schemes documented in [RC5].
Table “Intel IPP RC5 Functions” lists Intel IPP RC5 functions.
| Function Base Name | Operation |
|---|---|
| Functions for 64-bit Block Size | |
| ARCFive64GetSize | Gets the size of the IppsARCFive64Speccontext. |
| ARCFive64Init | Initializes user-supplied memory as the IppsARCFive64Spec context for future use. |
| ARCFive64Pack, ARCFive64Unpack | Packs/unpacks the ARCFive64Spec context into/from a user-defined buffer. |
| ARCFive64EncryptECB | Encrypts a variable length data stream using the RC5 cipher with 64-bit block size in the ECB mode. |
| ARCFive64DecryptECB | Decrypts a variable length data stream using the RC5 cipher with 64-bit block size in the ECB mode. |
| ARCFive64EncryptCBC | Encrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CBC mode. |
| ARCFive64DecryptCBC | Decrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CBC mode. |
| ARCFive64EncryptCFB | Encrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CFB mode. |
| ARCFive64DecryptCFB | Decrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CFB mode. |
| ARCFive64EncryptOFB | Encrypts a variable length data stream using the RC5 cipher with 64-bit block size in the OFB mode. |
| ARCFive64DecryptOFB | Decrypts a variable length data stream using the RC5 cipher with 64-bit block size in the OFB mode. |
| ARCFive64EncryptCTR | Encrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CTR mode. |
| ARCFive64DecryptCTR | Decrypts a variable length data stream using the RC5 cipher with 64-bit block size in the CTR mode. |
| Functions for 128-bit Block Size | |
| ARCFive128GetSize | Gets the size of the IppsARCFive128Spec context. |
| ARCFive128Init | Initializes user-supplied memory as the IppsARCFive128Spec context for future use. |
| ARCFive128Pack/ARCFive128Unpack | Packs/unpacks the ARCFive128Spec context into/from a user-defined buffer. |
| ARCFive128EncryptECB | Encrypts a variable length data stream using the RC5 cipher with 128-bit block size in the ECB mode. |
| ARCFive128DecryptECB | Decrypts a variable length data stream using the RC5 cipher with 128-bit block size in the ECB mode. |
| ARCFive128EncryptCBC | Encrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CBC mode. |
| ARCFive128DecryptCBC | Decrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CBC mode. |
| ARCFive128EncryptCFB | Encrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CFB mode. |
| ARCFive128DecryptCFB | Decrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CFB mode. |
| ARCFive128EncryptOFB | Encrypts a variable length data stream using the RC5 cipher with 128-bit block size in the OFB mode. |
| ARCFive128DecryptOFB | Decrypts a variable length data stream using the RC5 cipher with 128-bit block size in the OFB mode. |
| ARCFive128EncryptCTR | Encrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CTR mode. |
| ARCFive128DecryptCTR | Decrypts a variable length data stream using the RC5 cipher with 128-bit block size in the CTR mode. |
Throughout this section, the functions for the RC5 cipher with 64-bit block size employ the context IppsARCFive64Spec and the functions for the RC5 cipher with 128-bit block size employ the context IppsARCFive128Spec. These contexts serve as operational vehicles to carry variables needed to accomplish RC5 encryption/decryption, namely the number of rounds and expanded key table S.
Once the respective initialization function generates these variables, the functions for ECB, CBC, CFB, and other modes are ready for either encrypting or decrypting the streaming data with the specified padding scheme.
The application code for conducting a typical encryption in the CBC mode using the RC5 cipher with 64-bit block size should follow the sequence of operations outlined below:
- Get the size required to configure the context IppsARCFive64Spec by calling the function ARCFive64GetSize.
- Allocate a buffer whose size is not less than the function ARCFive64GetSize returns by calling the memory allocation service function of the operating system.
- Initialize the context IppsARCFive64Spec *pCtx by calling the function ARCFive64Init with the allocated buffer and the respective RC5 cipher key of the specified size.
- Specify the initialization vector and the padding scheme and then call the function ARCFive64EncryptCBC to encrypt the input data stream using the RC5 cipher in the CBC mode.
- Release the memory allocated to the buffer by calling the respective operating system function.
Note
Similar procedure can be applied for ECB, CFB, OFB, and CTR modes of operation as well as the RC5 cipher with 128-bit block size.
The ARCFive64Spec and ARCFive128Spec contexts are position-dependent. The ARCFive64Pack/ARCFive64Unpack and ARCFive128Pack/ARCFive128Unpack functions transform the respective position-dependent context to a position-independent form and vice versa.