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<a name="Using-cryptographic-functions"></a>
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<p>
Next: <a href="Handle_002dindependent-functions.html#Handle_002dindependent-functions" accesskey="n" rel="next">Handle-independent functions</a>, Previous: <a href="Working-with-keys.html#Working-with-keys" accesskey="p" rel="prev">Working with keys</a>, Up: <a href="AC-Interface.html#AC-Interface" accesskey="u" rel="up">AC Interface</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="Using-cryptographic-functions-1"></a>
<h4 class="subsection">6.6.6 Using cryptographic functions</h4>

<p>The following flags might be relevant:
</p>
<dl compact="compact">
<dt><code>GCRY_AC_FLAG_NO_BLINDING</code></dt>
<dd><p>Disable any blinding, which might be supported by the chosen
algorithm; blinding is the default.
</p></dd>
</dl>

<p>There exist two kinds of cryptographic functions available through the
ac interface: primitives, and high-level functions.
</p>
<p>Primitives deal with MPIs (data sets) directly; what they provide is
direct access to the cryptographic operations provided by an algorithm
implementation.
</p>
<p>High-level functions deal with octet strings, according to a specified
&ldquo;scheme&rdquo;.  Schemes make use of &ldquo;encoding methods&rdquo;, which are
responsible for converting the provided octet strings into MPIs, which
are then forwared to the cryptographic primitives.  Since schemes are
to be used for a special purpose in order to achieve a particular
security goal, there exist &ldquo;encryption schemes&rdquo; and &ldquo;signature
schemes&rdquo;.  Encoding methods can be used seperately or implicitly
through schemes.
</p>
<p>What follows is a description of the cryptographic primitives.
</p>
<dl>
<dt><a name="index-gcry_005fac_005fdata_005fencrypt"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_encrypt</strong> <em>(gcry_ac_handle_t <var>handle</var>, unsigned int <var>flags</var>, gcry_ac_key_t <var>key</var>, gcry_mpi_t <var>data_plain</var>, gcry_ac_data_t *<var>data_encrypted</var>)</em></dt>
<dd><p>Encrypts the plain text MPI value <var>data_plain</var> with the key public
<var>key</var> under the control of the flags <var>flags</var> and stores the
resulting data set into <var>data_encrypted</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fdecrypt"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_decrypt</strong> <em>(gcry_ac_handle_t <var>handle</var>, unsigned int <var>flags</var>, gcry_ac_key_t <var>key</var>, gcry_mpi_t *<var>data_plain</var>, gcry_ac_data_t <var>data_encrypted</var>)</em></dt>
<dd><p>Decrypts the encrypted data contained in the data set
<var>data_encrypted</var> with the secret key KEY under the control of the
flags <var>flags</var> and stores the resulting plain text MPI value in
<var>DATA_PLAIN</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fsign"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_sign</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_key_t <var>key</var>, gcry_mpi_t <var>data</var>, gcry_ac_data_t *<var>data_signature</var>)</em></dt>
<dd><p>Signs the data contained in <var>data</var> with the secret key <var>key</var>
and stores the resulting signature in the data set
<var>data_signature</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fverify"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_verify</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_key_t <var>key</var>, gcry_mpi_t <var>data</var>, gcry_ac_data_t <var>data_signature</var>)</em></dt>
<dd><p>Verifies that the signature contained in the data set
<var>data_signature</var> is indeed the result of signing the data
contained in <var>data</var> with the secret key belonging to the public
key <var>key</var>.
</p></dd></dl>

<p>What follows is a description of the high-level functions.
</p>
<p>The type &ldquo;gcry_ac_em_t&rdquo; is used for specifying encoding methods; the
following methods are supported:
</p>
<dl compact="compact">
<dt><code>GCRY_AC_EME_PKCS_V1_5</code></dt>
<dd><p>PKCS-V1_5 Encoding Method for Encryption.  Options must be provided
through a pointer to a correctly initialized object of type
gcry_ac_eme_pkcs_v1_5_t.
</p>
</dd>
<dt><code>GCRY_AC_EMSA_PKCS_V1_5</code></dt>
<dd><p>PKCS-V1_5 Encoding Method for Signatures with Appendix.  Options must
be provided through a pointer to a correctly initialized object of
type gcry_ac_emsa_pkcs_v1_5_t.
</p></dd>
</dl>

<p>Option structure types:
</p>
<dl compact="compact">
<dt><code>gcry_ac_eme_pkcs_v1_5_t</code></dt>
<dd><dl compact="compact">
<dt><code>gcry_ac_key_t key</code></dt>
<dt><code>gcry_ac_handle_t handle</code></dt>
</dl>
</dd>
<dt><code>gcry_ac_emsa_pkcs_v1_5_t</code></dt>
<dd><dl compact="compact">
<dt><code>gcry_md_algo_t md</code></dt>
<dt><code>size_t em_n</code></dt>
</dl>
</dd>
</dl>

<p>Encoding methods can be used directly through the following functions:
</p>
<dl>
<dt><a name="index-gcry_005fac_005fdata_005fencode"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_encode</strong> <em>(gcry_ac_em_t <var>method</var>, unsigned int <var>flags</var>, void *<var>options</var>, unsigned char *<var>m</var>, size_t <var>m_n</var>, unsigned char **<var>em</var>, size_t *<var>em_n</var>)</em></dt>
<dd><p>Encodes the message contained in <var>m</var> of size <var>m_n</var> according
to <var>method</var>, <var>flags</var> and <var>options</var>.  The newly created
encoded message is stored in <var>em</var> and <var>em_n</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fdecode"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_decode</strong> <em>(gcry_ac_em_t <var>method</var>, unsigned int <var>flags</var>, void *<var>options</var>, unsigned char *<var>em</var>, size_t <var>em_n</var>, unsigned char **<var>m</var>, size_t *<var>m_n</var>)</em></dt>
<dd><p>Decodes the message contained in <var>em</var> of size <var>em_n</var> according
to <var>method</var>, <var>flags</var> and <var>options</var>.  The newly created
decoded message is stored in <var>m</var> and <var>m_n</var>.
</p></dd></dl>

<p>The type &ldquo;gcry_ac_scheme_t&rdquo; is used for specifying schemes; the
following schemes are supported:
</p>
<dl compact="compact">
<dt><code>GCRY_AC_ES_PKCS_V1_5</code></dt>
<dd><p>PKCS-V1_5 Encryption Scheme.  No options can be provided.
</p></dd>
<dt><code>GCRY_AC_SSA_PKCS_V1_5</code></dt>
<dd><p>PKCS-V1_5 Signature Scheme (with Appendix).  Options can be provided
through a pointer to a correctly initialized object of type
gcry_ac_ssa_pkcs_v1_5_t.
</p></dd>
</dl>

<p>Option structure types:
</p>
<dl compact="compact">
<dt><code>gcry_ac_ssa_pkcs_v1_5_t</code></dt>
<dd><dl compact="compact">
<dt><code>gcry_md_algo_t md</code></dt>
</dl>
</dd>
</dl>

<p>The functions implementing schemes:
</p>
<dl>
<dt><a name="index-gcry_005fac_005fdata_005fencrypt_005fscheme"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_encrypt_scheme</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_scheme_t <var>scheme</var>, unsigned int <var>flags</var>, void *<var>opts</var>, gcry_ac_key_t <var>key</var>, gcry_ac_io_t *<var>io_message</var>, gcry_ac_io_t *<var>io_cipher</var>)</em></dt>
<dd><p>Encrypts the plain text readable from <var>io_message</var> through
<var>handle</var> with the public key <var>key</var> according to <var>scheme</var>,
<var>flags</var> and <var>opts</var>.  If <var>opts</var> is not NULL, it has to be a
pointer to a structure specific to the chosen scheme (gcry_ac_es_*_t).
The encrypted message is written to <var>io_cipher</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fdecrypt_005fscheme"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_decrypt_scheme</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_scheme_t <var>scheme</var>, unsigned int <var>flags</var>, void *<var>opts</var>, gcry_ac_key_t <var>key</var>, gcry_ac_io_t *<var>io_cipher</var>, gcry_ac_io_t *<var>io_message</var>)</em></dt>
<dd><p>Decrypts the cipher text readable from <var>io_cipher</var> through
<var>handle</var> with the secret key <var>key</var> according to <var>scheme</var>,
<var>flags</var> and <var>opts</var>.  If <var>opts</var> is not NULL, it has to be a
pointer to a structure specific to the chosen scheme (gcry_ac_es_*_t).
The decrypted message is written to <var>io_message</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fsign_005fscheme"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_sign_scheme</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_scheme_t <var>scheme</var>, unsigned int <var>flags</var>, void *<var>opts</var>, gcry_ac_key_t <var>key</var>, gcry_ac_io_t *<var>io_message</var>, gcry_ac_io_t *<var>io_signature</var>)</em></dt>
<dd><p>Signs the message readable from <var>io_message</var> through <var>handle</var>
with the secret key <var>key</var> according to <var>scheme</var>, <var>flags</var>
and <var>opts</var>.  If <var>opts</var> is not NULL, it has to be a pointer to
a structure specific to the chosen scheme (gcry_ac_ssa_*_t).  The
signature is written to <var>io_signature</var>.
</p></dd></dl>

<dl>
<dt><a name="index-gcry_005fac_005fdata_005fverify_005fscheme"></a>Function: <em>gcry_error_t</em> <strong>gcry_ac_data_verify_scheme</strong> <em>(gcry_ac_handle_t <var>handle</var>, gcry_ac_scheme_t <var>scheme</var>, unsigned int <var>flags</var>, void *<var>opts</var>, gcry_ac_key_t <var>key</var>, gcry_ac_io_t *<var>io_message</var>, gcry_ac_io_t *<var>io_signature</var>)</em></dt>
<dd><p>Verifies through <var>handle</var> that the signature readable from
<var>io_signature</var> is indeed the result of signing the message
readable from <var>io_message</var> with the secret key belonging to the
public key <var>key</var> according to <var>scheme</var> and <var>opts</var>.  If
<var>opts</var> is not NULL, it has to be an anonymous structure
(gcry_ac_ssa_*_t) specific to the chosen scheme.
</p></dd></dl>

<hr>
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