Performing RSA Operations
214 RSA BSAFE Crypto-C Developer’s Guide
Performing RSA Operations
The RSA algorithm is a public-key algorithm that relies on the difficulty of factoring a
number that is the product of two large primes. If you are not familiar with the RSA
algorithm and terminology, you may want to read “The RSA Algorithm” on page 51
before you continue.
The algorithm chooser used throughout the sections concerning executing the RSA
algorithm can be found in “Algorithm Choosers” on page 116.
The example in this section corresponds to the file rsapkcs.c.
Note: For an example of how to perform RSA operations in conformance with the
ANSI X9.31 standard, see Chapter 9, “Putting It All Together: An X9.31
Example” on page313. The example in Chapter 9 is similar to this one;
however, due to the additional constraints required by X9.31, some of the
operations are more time-consuming.

Generating a Key Pair

Before you can encrypt and decrypt, you need a key pair. The key pair consists of a
private key and its associated public key. Generating a key pair is not trivial. The RSA
algorithm relies on very large prime numbers, which are produced during key pair
generation. This could be fairly time-consuming, so we recommend you use a
surrender context. The surrender context used below is the one in “The Surrender
Context” on page118.
Most Crypto-C operations follow the six-step procedure outlined in the “Introductory
Example” on page9. Generating a key pair needs only five of the steps; there is no
Update call.
Step 1: Creating An Algorithm Object
Declare a variable to be B_ALGORITHM_OBJ. As defined in the function prototype in
Chapter 4 of the Reference Manual, its address is the argument for
B_CreateAlgorithmObject:
B_ALGORITHM_OBJ keypairGenerator = (B_ALGORITHM_OBJ)NULL_PTR;
if ((status = B_CreateAlgorithmObject (&keypairGenerator)) != 0)
break;