RSA Security Projection Television 5.2.2 Manual de usuario descargar pdf (Pagina 305)

Chapter 7 Public-Key Operations 283

Performing Elliptic Curve Operations

You must allocate space to hold the results of Phase 1 and Phase 2. The largest size of

Phase 1 output you can get is one byte larger than twice the field element size. For

Phase 2, the size of the output should be the same as the field element size. (See the

Reference Manual Chapter 2 entry for

AI_EC_DHKeyAgree for details.)

You can get the field element size using Alice’s elliptic curve parameters. Since you

have the parameters in the

A_EC_PARAMS structure

ecParams

, look at the

fieldElementBits

field, which gives you the required information. A simple

manipulation gives you the field element length in bytes:

Step 4: Phase 1

During this phase, each party computes a private value and a public value. The

private value is secret and currently cannot be accessed though the Crypto-C API. The

public value should be transported to the other party. Note that you will have to

supply a properly initialized random algorithm as the fifth argument to

B_KeyAgreePhase1:

if ((status = B_KeyAgreeInit(alice, (B_KEY_OBJ)NULL_PTR, EC_DH_CHOOSER,

(A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

unsigned int fieldElementLen, maxPhase1Len, maxPhase2Len;

fieldElementLen = (ecParams->fieldElementBits + 7) / 8;

maxPhase1Len = (fieldElementLen * 2);

maxPhase2Len = fieldElementLen;

unsigned char *alicePublicValue = NULL_PTR;

unsigned int alicePublicValueLen;

alicePublicValue = T_malloc(maxPhase1Len);

if ((status = (alicePublicValue == NULL_PTR)) != 0)

break;

if ((status = B_KeyAgreePhase1(alice, alicePublicValue,

&alicePublicValueLen, maxPhase1Len,

randomAlgorithm,

(A_SURRENDER_CTX *)NULL_PTR)) != 0)

break;

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RSA Security Projection Television 5.2.2 Manual de usuario Pagina 305