7.2 Used S-expressions

Libgcrypt's API for asymmetric cryptography is based on data structures called S-expressions (see XXXX) and does not work with contexts as most of the other building blocks of Libgcrypt do.

The following information are stored in S-expressions:

keys

plain text data

encrypted data

signatures

To describe how Libgcrypt expect keys, we use examples. Note that words in uppercase indicate parameters whereas lowercase words are literals.

Note that all MPI (big integer) values are expected to be in GCRYMPI_FMT_USG format. An easy way to create S-expressions is by using gcry_sexp_build which allows to pass a string with printf-like escapes to insert MPI values.

• RSA key parameters: Parameters used with an RSA key.
• DSA key parameters: Parameters used with a DSA key.
• ECC key parameters: Parameters used with ECC keys.