PBC Library Manual 0.5.11 - Stanford Crypto Group

Chapter 3. Pairing functions
An application should first initialize a pairing object. This causes PBC to setup curves, groups and other
mathematical miscellany. After that, elements can be initialized and manipulated for cryptographic
operations.
Parameters for various pairings are included with the PBC library distribution in the param subdirectory,
and some are suitable for cryptographic use. Some programs in the gen subdirectory may be used to
generate parameters (see Chapter 7). Also, see the PBC website for many more pairing parameters.
Pairings involve three groups of prime order. The PBC library calls them G1, G2, and GT, and calls the
order r. The pairing is a bilinear map that takes two elements as input, one from G1 and one from G2,
and outputs an element of GT.
The elements of G2 are at least as long as G1; G1 is guaranteed to be the shorter of the two. Sometimes
G1 and G2 are the same group (i.e. the pairing is symmetric) so their elements can be mixed freely. In
this case the pairing_is_symmetric function returns 1.
Bilinear pairings are stored in the data type pairing_t. Functions that operate on them start with
pairing_.
3.1. Initializing pairings
To initialize a pairing from an ASCIIZ string:
pairing_t pairing;
pairing_init_set_str(pairing, s); // Where s is a char *.
The string s holds pairing parameters in a text format. The param subdirectory contains several
examples.
Alternatively, call:
pairing_t pairing;
pairing_init_pbc_param(pairing, param);
where param is an initialized pbc_param_t (see Chapter 5).
int pairing_init_set_str(pairing_t pairing, const char *s)
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