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Chapter 7 Public-Key Operations 255
Performing Diffie-Hellman Key Agreement
Crypto-C returns a pointer to where that information resides, not the information. As
soon as the object that contains that information is destroyed, the information will no
longer be accessible. Therefore, once you get the pointer to that information, copy it
into your own buffer:
In summary, generate the parameters, get the algorithm
info
in BER format with
B_GetAlgorithmInfo and AI_DHKeyAgreeBER, encode the BER data into ASCII format
and send it to the Diffie-Hellman key agreement participants.
Note: The conversion into BER or DER is known as BER-encoding or DER-
encoding, and the conversion between binary to ASCII is known as encoding
and decoding. This may get confusing, but the word encoding without a BER
in front of it generally means binary to ASCII. If the encoding is BER- or DER-
encoding, the BER or DER should be explicitly stated.
Format of info returned by
B_GetAlgorithmInfo:
pointer to an
ITEM structure which gives the address and length of the DER-encoded
algorithm identifier.
ITEM *cryptocDHParametersBER;
ITEM myDHParametersBER;
myDHParametersBER.data = NULL_PTR;
if ((status = B_GetAlgorithmInfo
((POINTER *)&cryptocDHParametersBER, myDHParametersObj,
AI_DHKeyAgreeBER)) != 0)
break;
myDHParametersBER.len = cryptocDHParametersBER->len;
myDHParametersBER.data = T_malloc (myDHParametersBER.len);
if ((status = (myDHParametersBER.data == NULL_PTR)) != 0)
break;
T_memcpy (myDHParametersBER.data, cryptocDHParametersBER->data,
myDHParametersBER.len);