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<title>GnuTLS 3.2.1: Accessing objects that require a PIN</title>

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<a name="Accessing-objects-that-require-a-PIN"></a>
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<p>
Next: <a href="Reading-objects.html#Reading-objects" accesskey="n" rel="next">Reading objects</a>, Previous: <a href="PKCS11-Initialization.html#PKCS11-Initialization" accesskey="p" rel="previous">PKCS11 Initialization</a>, Up: <a href="Smart-cards-and-HSMs.html#Smart-cards-and-HSMs" accesskey="u" rel="up">Smart cards and HSMs</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="Accessing-objects-that-require-a-PIN-1"></a>
<h4 class="subsection">5.2.2 Accessing objects that require a PIN</h4>

<p>Objects stored in token such as a private keys are typically protected
from access by a PIN or password. This PIN may be required to either read
the object (if allowed) or to perform operations with it. To allow obtaining
the PIN when accessing a protected object, as well as probe
the user to insert the token the following functions allow to set a callback.
</p>
<dl compact="compact">
<dt><code><var>void</var> <a href="PKCS-11-API.html#gnutls_005fpkcs11_005fset_005ftoken_005ffunction">gnutls_pkcs11_set_token_function</a> (gnutls_pkcs11_token_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>void</var> <a href="PKCS-11-API.html#gnutls_005fpkcs11_005fset_005fpin_005ffunction">gnutls_pkcs11_set_pin_function</a> (gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>int</var> <a href="PKCS-11-API.html#gnutls_005fpkcs11_005fadd_005fprovider">gnutls_pkcs11_add_provider</a> (const char * <var>name</var>, const char * <var>params</var>)</code></dt>
<dt><code><var>gnutls_pin_callback_t</var> <a href="PKCS-11-API.html#gnutls_005fpkcs11_005fget_005fpin_005ffunction">gnutls_pkcs11_get_pin_function</a> (void ** <var>userdata</var>)</code></dt>
</dl>

<p>The callback is of type <code>gnutls_pin_callback_t</code> and will have as
input the provided userdata, the PIN attempt number, a URL describing the
token, a label describing the object and flags. The PIN must be at most 
of <code>pin_max</code> size and must be copied to pin variable. The function must
return 0 on success or a negative error code otherwise.
</p>
<pre class="verbatim">typedef int (*gnutls_pin_callback_t) (void *userdata, int attempt,
                                      const char *token_url,
                                      const char *token_label,
                                      unsigned int flags,
                                      char *pin, size_t pin_max);
</pre>
<p>The flags are of <code>gnutls_pin_flag_t</code> type and are explained below.
</p>
<div class="float"><a name="gnutls_005fpin_005fflag_005ft"></a>


<dl compact="compact">
<dt><code>GNUTLS_PIN_USER</code></dt>
<dd><p>The PIN for the user.
</p></dd>
<dt><code>GNUTLS_PIN_SO</code></dt>
<dd><p>The PIN for the security officer (admin).
</p></dd>
<dt><code>GNUTLS_PIN_FINAL_TRY</code></dt>
<dd><p>This is the final try before blocking.
</p></dd>
<dt><code>GNUTLS_PIN_COUNT_LOW</code></dt>
<dd><p>Few tries remain before token blocks.
</p></dd>
<dt><code>GNUTLS_PIN_CONTEXT_SPECIFIC</code></dt>
<dd><p>The PIN is for a specific action and key like signing.
</p></dd>
<dt><code>GNUTLS_PIN_WRONG</code></dt>
<dd><p>Last given PIN was not correct.
</p></dd>
</dl>

<div class="float-caption"><p><strong>Figure 5.2: </strong>The <code>gnutls_pin_flag_t</code> enumeration.</p></div></div>
<p>Note that due to limitations of <acronym>PKCS</acronym> #11 there are issues when multiple libraries 
are sharing a module. To avoid this problem GnuTLS uses <acronym>p11-kit</acronym>
that provides a middleware to control access to resources over the
multiple users.
</p>
<p>To avoid conflicts with multiple registered callbacks for PIN functions,
<a href="PKCS-11-API.html#gnutls_005fpkcs11_005fget_005fpin_005ffunction">gnutls_pkcs11_get_pin_function</a> may be used to check for any previously
set functions. In addition context specific PIN functions are allowed, e.g., by
using functions below.
</p>
<dl compact="compact">
<dt><code><var>void</var> <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fpin_005ffunction">gnutls_certificate_set_pin_function</a> (gnutls_certificate_credentials_t <var>cred</var>, gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>void</var> <a href="Abstract-key-API.html#gnutls_005fpubkey_005fset_005fpin_005ffunction">gnutls_pubkey_set_pin_function</a> (gnutls_pubkey_t <var>key</var>, gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>void</var> <a href="Abstract-key-API.html#gnutls_005fprivkey_005fset_005fpin_005ffunction">gnutls_privkey_set_pin_function</a> (gnutls_privkey_t <var>key</var>, gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>void</var> <a href="PKCS-11-API.html#gnutls_005fpkcs11_005fobj_005fset_005fpin_005ffunction">gnutls_pkcs11_obj_set_pin_function</a> (gnutls_pkcs11_obj_t <var>obj</var>, gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
<dt><code><var>void</var> <a href="X509-certificate-API.html#gnutls_005fx509_005fcrt_005fset_005fpin_005ffunction">gnutls_x509_crt_set_pin_function</a> (gnutls_x509_crt_t <var>crt</var>, gnutls_pin_callback_t <var>fn</var>, void * <var>userdata</var>)</code></dt>
</dl>

<hr>
<div class="header">
<p>
Next: <a href="Reading-objects.html#Reading-objects" accesskey="n" rel="next">Reading objects</a>, Previous: <a href="PKCS11-Initialization.html#PKCS11-Initialization" accesskey="p" rel="previous">PKCS11 Initialization</a>, Up: <a href="Smart-cards-and-HSMs.html#Smart-cards-and-HSMs" accesskey="u" rel="up">Smart cards and HSMs</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
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