diff --git a/Makefile.am b/Makefile.am
index 761df66..0b7a060 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -114,7 +114,9 @@ EXTRA_DIST = \
 	jni/Application.mk \
 	src/tls_schannel.c \
 	tests/cert.pem \
+	tests/cert.pfx \
 	tests/key.pem \
+	tests/key_encrypted.pem \
 	tests/res_query_dump.c
 
 ## Examples
diff --git a/examples/complex.c b/examples/complex.c
index 00305ee..67c5d01 100644
--- a/examples/complex.c
+++ b/examples/complex.c
@@ -12,6 +12,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <unistd.h>
 
 #ifdef _WIN32
 #include <winsock2.h>
@@ -93,6 +94,52 @@ static int certfail_handler(const xmpp_tlscert_t *cert,
     return read_char[0] == 'y' || read_char[0] == 'Y';
 }
 
+static int
+password_callback(char *pw, size_t pw_max, const char *fname, void *userdata)
+{
+    (void)userdata;
+    /* when using an encrypted keyfile, we get asked multiple times for the
+     * password ... cache it until we're connected
+     */
+    static struct {
+        char pass[256];
+        unsigned char hash[XMPP_SHA1_DIGEST_SIZE];
+        size_t passlen, fnamelen;
+        unsigned count;
+    } password_cache;
+    int ret = -1;
+    unsigned char hash[XMPP_SHA1_DIGEST_SIZE];
+
+    size_t fname_len = strlen(fname);
+    xmpp_sha1_digest((void *)fname, fname_len, hash);
+    if (fname_len && fname_len == password_cache.fnamelen &&
+        memcmp(hash, password_cache.hash, sizeof(hash)) == 0) {
+        if (password_cache.passlen && --password_cache.count) {
+            memcpy(pw, password_cache.pass, password_cache.passlen + 1);
+            ret = password_cache.passlen;
+            if (!password_cache.count)
+                memset(&password_cache, 0, sizeof(password_cache));
+            return ret;
+        }
+    }
+    printf("Trying to unlock %s\n", fname);
+    char *pass = getpass("Please enter password: ");
+    if (!pass)
+        return -1;
+    size_t passlen = strlen(pass);
+    if (passlen < pw_max) {
+        memcpy(pw, pass, passlen + 1);
+        ret = passlen;
+        memcpy(password_cache.pass, pass, passlen + 1);
+        password_cache.passlen = passlen;
+        password_cache.count = 6;
+        memcpy(password_cache.hash, hash, sizeof(hash));
+        password_cache.fnamelen = fname_len;
+    }
+    memset(pass, 0, passlen);
+    return ret;
+}
+
 static int sockopt_cb(xmpp_conn_t *conn, void *socket)
 {
     int timeout = KA_TIMEOUT;
@@ -181,7 +228,7 @@ static void usage(int exit_code)
             "  --jid <jid>              The JID to use to authenticate.\n"
             "  --pass <pass>            The password of the JID.\n"
             "  --tls-cert <cert>        Path to client certificate.\n"
-            "  --tls-key <key>          Path to private key.\n\n"
+            "  --tls-key <key>          Path to private key or P12 file.\n\n"
             "  --capath <path>          Path to an additional CA trust store "
             "(directory).\n"
             "  --cafile <path>          Path to an additional CA trust store "
@@ -247,7 +294,7 @@ int main(int argc, char **argv)
         else
             break;
     }
-    if ((!jid && (!cert || !key)) || (argc - i) > 2) {
+    if ((!jid && !key) || (argc - i) > 2) {
         usage(1);
     }
 
@@ -279,8 +326,10 @@ int main(int argc, char **argv)
     if (tcp_keepalive)
         xmpp_conn_set_sockopt_callback(conn, sockopt_cb);
 
+    /* ask for a password if key is protected */
+    xmpp_conn_set_password_callback(conn, password_callback, conn);
     /* setup authentication information */
-    if (cert && key) {
+    if (key) {
         xmpp_conn_set_client_cert(conn, cert, key);
     }
     if (jid)
diff --git a/src/auth.c b/src/auth.c
index eaaf3cc..24a6291 100644
--- a/src/auth.c
+++ b/src/auth.c
@@ -242,7 +242,7 @@ _handle_features(xmpp_conn_t *conn, xmpp_stanza_t *stanza, void *userdata)
                 if (strcasecmp(text, "PLAIN") == 0)
                     conn->sasl_support |= SASL_MASK_PLAIN;
                 else if (strcasecmp(text, "EXTERNAL") == 0 &&
-                         conn->tls_client_cert)
+                         (conn->tls_client_cert || conn->tls_client_key))
                     conn->sasl_support |= SASL_MASK_EXTERNAL;
                 else if (strcasecmp(text, "DIGEST-MD5") == 0)
                     conn->sasl_support |= SASL_MASK_DIGESTMD5;
diff --git a/src/common.h b/src/common.h
index 1b60b1b..964fb5f 100644
--- a/src/common.h
+++ b/src/common.h
@@ -192,6 +192,8 @@ struct _xmpp_conn_t {
     int auth_legacy_enabled;
     int secured; /* set when stream is secured with TLS */
     xmpp_certfail_handler certfail_handler;
+    xmpp_password_callback password_callback;
+    void *password_callback_userdata;
 
     /* if server returns <bind/> or <session/> we must do them */
     int bind_required;
diff --git a/src/conn.c b/src/conn.c
index b9e1ffe..261c3cb 100644
--- a/src/conn.c
+++ b/src/conn.c
@@ -182,6 +182,8 @@ xmpp_conn_t *xmpp_conn_new(xmpp_ctx_t *ctx)
         conn->auth_legacy_enabled = 0;
         conn->secured = 0;
         conn->certfail_handler = NULL;
+        conn->password_callback = NULL;
+        conn->password_callback_userdata = NULL;
 
         conn->bind_required = 0;
         conn->session_required = 0;
@@ -492,15 +494,38 @@ xmpp_tlscert_t *xmpp_conn_get_peer_cert(xmpp_conn_t *const conn)
     return tls_peer_cert(conn);
 }
 
-/** Set the Client Certificate and Private Key that will be bound to the
- *  connection. If any of the both was previously set, it will be discarded.
- *  This should not be used after a connection is created.  The function will
- *  make a copy of the strings passed in.
- *  Currently only non-encrypted Private Keys are supported.
+/** Set the Callback function which will be called when the TLS stack can't
+ *  decrypt a password protected key file.
+ *
+ *  @param conn a   Strophe connection object
+ *  @param cb       The callback function that shall be called
+ *  @param userdata An opaque data pointer that will be passed to the callback
+ *
+ *  @ingroup TLS
+ */
+void xmpp_conn_set_password_callback(xmpp_conn_t *conn,
+                                     xmpp_password_callback cb,
+                                     void *userdata)
+{
+    conn->password_callback = cb;
+    conn->password_callback_userdata = userdata;
+}
+
+/** Set the Client Certificate and Private Key or PKCS#12 encoded file that
+ *  will be bound to the connection. If any of them was previously set, it
+ *  will be discarded. This should not be used after a connection is created.
+ *  The function will make a copy of the strings passed in.
+ *
+ *  In case the Private Key is encrypted, a callback must be set via
+ *  \ref xmpp_conn_set_password_callback so the TLS stack can retrieve the
+ *  password.
+ *
+ *  In case one wants to use a PKCS#12 encoded file, it must be passed via
+ *  the `key` parameter and `cert` must be NULL.
  *
  *  @param conn a Strophe connection object
  *  @param cert path to a certificate file
- *  @param key path to a private key file
+ *  @param key path to a private key file or a P12 file
  *
  *  @ingroup TLS
  */
@@ -511,7 +536,10 @@ void xmpp_conn_set_client_cert(xmpp_conn_t *const conn,
     strophe_debug(conn->ctx, "conn", "set client cert %s %s", cert, key);
     if (conn->tls_client_cert)
         strophe_free(conn->ctx, conn->tls_client_cert);
-    conn->tls_client_cert = strophe_strdup(conn->ctx, cert);
+    if (cert)
+        conn->tls_client_cert = strophe_strdup(conn->ctx, cert);
+    else
+        conn->tls_client_cert = NULL;
     if (conn->tls_client_key)
         strophe_free(conn->ctx, conn->tls_client_key);
     conn->tls_client_key = strophe_strdup(conn->ctx, key);
@@ -620,7 +648,7 @@ int xmpp_connect_client(xmpp_conn_t *conn,
     int found = XMPP_DOMAIN_NOT_FOUND;
     int rc;
 
-    if (!conn->jid && conn->tls_client_cert) {
+    if (!conn->jid && (conn->tls_client_cert || conn->tls_client_key)) {
         if (tls_id_on_xmppaddr_num(conn) != 1) {
             strophe_debug(conn->ctx, "xmpp",
                           "Client certificate contains multiple or no xmppAddr "
diff --git a/src/tls_gnutls.c b/src/tls_gnutls.c
index b56810e..7c506f5 100644
--- a/src/tls_gnutls.c
+++ b/src/tls_gnutls.c
@@ -17,6 +17,8 @@
 #include <gnutls/gnutls.h>
 #include <gnutls/x509.h>
 #include <gnutls/x509-ext.h>
+#include <gnutls/pkcs11.h>
+#include <gnutls/pkcs12.h>
 
 #include "common.h"
 #include "tls.h"
@@ -47,10 +49,30 @@ void tls_shutdown(void)
     gnutls_global_deinit();
 }
 
-static gnutls_x509_crt_t _tls_load_cert(xmpp_conn_t *conn)
+static int _tls_password_callback(void *userdata,
+                                  int attempt,
+                                  const char *token_url,
+                                  const char *token_label,
+                                  unsigned int flags,
+                                  char *pin,
+                                  size_t pin_max)
+{
+    xmpp_conn_t *conn = userdata;
+    UNUSED(attempt);
+    UNUSED(token_url);
+    UNUSED(token_label);
+    UNUSED(flags);
+    if (!conn->password_callback) {
+        strophe_error(conn->ctx, "tls", "No password callback set");
+        return -1;
+    }
+    int ret = conn->password_callback(pin, pin_max, conn->tls_client_key,
+                                      conn->password_callback_userdata);
+    return ret > 0 ? 0 : GNUTLS_E_PKCS11_PIN_ERROR;
+}
+
+static gnutls_x509_crt_t _tls_load_cert_x509(xmpp_conn_t *conn)
 {
-    if (conn->tls && conn->tls->client_cert)
-        return conn->tls->client_cert;
     gnutls_x509_crt_t cert;
     gnutls_datum_t data;
     int res;
@@ -68,6 +90,64 @@ error_out:
     return NULL;
 }
 
+static gnutls_x509_crt_t _tls_load_cert_p12(xmpp_conn_t *conn)
+{
+    gnutls_pkcs12_t p12;
+    gnutls_x509_crt_t *cert;
+    gnutls_datum_t data;
+    gnutls_x509_privkey_t key;
+    unsigned int cert_num = 0;
+    if (gnutls_pkcs12_init(&p12) < 0)
+        return NULL;
+    if (gnutls_load_file(conn->tls_client_key, &data) < 0)
+        goto error_out;
+    if (gnutls_pkcs12_import(p12, &data, GNUTLS_X509_FMT_DER, 0) < 0)
+        goto error_out2;
+
+    char pass[GNUTLS_PKCS11_MAX_PIN_LEN];
+    pass[0] = '\0';
+    int passlen =
+        _tls_password_callback(conn, 0, NULL, NULL, 0, pass, sizeof(pass));
+    if (passlen < 0)
+        pass[0] = '\0';
+
+    int res = gnutls_pkcs12_simple_parse(p12, pass, &key, &cert, &cert_num,
+                                         NULL, NULL, NULL, 0);
+    gnutls_pkcs12_deinit(p12);
+    gnutls_free(data.data);
+    if (res < 0)
+        goto error_out;
+    gnutls_x509_privkey_deinit(key);
+    if (cert_num > 1) {
+        strophe_error(conn->ctx, "tls", "Can't handle stack of %u certs",
+                      cert_num);
+        goto error_out;
+    }
+    gnutls_x509_crt_t ret = *cert;
+    gnutls_free(cert);
+    return ret;
+error_out2:
+    gnutls_free(data.data);
+error_out:
+    if (cert) {
+        for (unsigned int n = 0; n < cert_num; ++n) {
+            gnutls_x509_crt_deinit(cert[n]);
+        }
+        gnutls_free(cert);
+    }
+    return NULL;
+}
+
+static gnutls_x509_crt_t _tls_load_cert(xmpp_conn_t *conn)
+{
+    if (conn->tls && conn->tls->client_cert)
+        return conn->tls->client_cert;
+    if (!conn->tls_client_cert && conn->tls_client_key) {
+        return _tls_load_cert_p12(conn);
+    }
+    return _tls_load_cert_x509(conn);
+}
+
 static void _tls_free_cert(xmpp_conn_t *conn, gnutls_x509_crt_t cert)
 {
     if (conn->tls && conn->tls->client_cert == cert)
@@ -269,12 +349,15 @@ static int _tls_verify(gnutls_session_t session)
 
     /* Return early if the Certificate is trusted
      * OR if we trust all Certificates */
-    if (status == 0 || tls->conn->tls_trust)
+    if (status == 0 || tls->conn->tls_trust) {
+        gnutls_free(out.data);
         return 0;
+    }
 
     if (!tls->conn->certfail_handler) {
         strophe_error(tls->ctx, "tls",
                       "No certfail handler set, canceling connection attempt");
+        gnutls_free(out.data);
         return -1;
     }
 
@@ -324,6 +407,9 @@ tls_t *tls_new(xmpp_conn_t *conn)
         gnutls_certificate_allocate_credentials(&tls->cred);
         tls_set_credentials(tls, NULL);
 
+        gnutls_certificate_set_pin_function(tls->cred, _tls_password_callback,
+                                            conn);
+
         if (conn->tls_client_cert && conn->tls_client_key) {
             tls->client_cert = _tls_load_cert(conn);
             if (!tls->client_cert) {
@@ -337,6 +423,15 @@ tls_t *tls_new(xmpp_conn_t *conn)
             gnutls_certificate_set_x509_key_file(
                 tls->cred, conn->tls_client_cert, conn->tls_client_key,
                 GNUTLS_X509_FMT_PEM);
+        } else if (conn->tls_client_key) {
+            char pass[GNUTLS_PKCS11_MAX_PIN_LEN];
+            pass[0] = '\0';
+            int passlen = _tls_password_callback(conn, 0, NULL, NULL, 0, pass,
+                                                 sizeof(pass));
+            if (passlen < 0)
+                pass[0] = '\0';
+            gnutls_certificate_set_x509_simple_pkcs12_file(
+                tls->cred, conn->tls_client_key, GNUTLS_X509_FMT_DER, pass);
         }
 
         gnutls_certificate_set_verify_function(tls->cred, _tls_verify);
diff --git a/src/tls_openssl.c b/src/tls_openssl.c
index ab962b6..4dde48b 100644
--- a/src/tls_openssl.c
+++ b/src/tls_openssl.c
@@ -26,6 +26,7 @@
 #include <openssl/err.h>
 #include <openssl/opensslv.h>
 #include <openssl/x509v3.h>
+#include <openssl/pkcs12.h>
 
 #include "common.h"
 #include "tls.h"
@@ -54,6 +55,30 @@ static const unsigned char *ASN1_STRING_get0_data(ASN1_STRING *asn1)
 }
 #endif
 
+#if OPENSSL_VERSION_NUMBER < 0x10100000L || defined LIBRESSL_VERSION_NUMBER
+static int SSL_CTX_use_cert_and_key(SSL_CTX *ctx,
+                                    X509 *x509,
+                                    EVP_PKEY *privatekey,
+                                    STACK_OF(X509) * chain,
+                                    int override)
+{
+    UNUSED(override);
+    if (!ctx)
+        return 0;
+    if (x509 && !SSL_CTX_use_certificate(ctx, x509))
+        return 0;
+    if (privatekey && !SSL_CTX_use_PrivateKey(ctx, privatekey))
+        return 0;
+#ifdef SSL_CTX_set1_chain
+    if (chain && !SSL_CTX_set1_chain(ctx, chain))
+        return 0;
+#else
+    UNUSED(chain);
+#endif
+    return 1;
+}
+#endif
+
 #if OPENSSL_VERSION_NUMBER < 0x10000000L
 static int GENERAL_NAME_get0_otherName(const GENERAL_NAME *gen,
                                        ASN1_OBJECT **poid,
@@ -90,6 +115,8 @@ static void _tls_set_error(tls_t *tls, int error);
 static void _tls_log_error(xmpp_ctx_t *ctx);
 static void _tls_dump_cert_info(tls_t *tls);
 static X509 *_tls_cert_read(xmpp_conn_t *conn);
+static X509 *
+_tls_cert_read_p12(xmpp_conn_t *conn, EVP_PKEY **pkey, STACK_OF(X509) * *ca);
 static int _tls_xaddr_nid(void);
 static int _tls_xmppaddr_to_string(GENERAL_NAME *name, char **res);
 static int _tls_dnsname_to_string(GENERAL_NAME *name, char **res);
@@ -260,8 +287,10 @@ char *tls_id_on_xmppaddr(xmpp_conn_t *conn, unsigned int n)
     char *ret = NULL;
     int i, j;
     GENERAL_NAMES *names = _tls_conn_get_names(conn);
-    if (!names)
+    if (!names) {
+        _tls_log_error(conn->ctx);
         return NULL;
+    }
     int num_names = sk_GENERAL_NAME_num(names);
     for (i = j = 0; i < num_names; ++i) {
         char *res;
@@ -288,8 +317,10 @@ unsigned int tls_id_on_xmppaddr_num(xmpp_conn_t *conn)
 {
     unsigned int ret = 0;
     GENERAL_NAMES *names = _tls_conn_get_names(conn);
-    if (!names)
+    if (!names) {
+        _tls_log_error(conn->ctx);
         return 0;
+    }
     int j, num_names = sk_GENERAL_NAME_num(names);
     for (j = 0; j < num_names; ++j) {
         GENERAL_NAME *name = sk_GENERAL_NAME_value(names, j);
@@ -355,18 +386,16 @@ _get_fingerprint(const xmpp_ctx_t *ctx, X509 *err_cert, xmpp_cert_element_t el)
 static char *
 _get_alg(const xmpp_ctx_t *ctx, X509 *err_cert, xmpp_cert_element_t el)
 {
-    int rc, alg_nid = NID_undef;
+    int alg_nid = NID_undef;
 
     switch (el) {
     case XMPP_CERT_KEYALG: {
 #if OPENSSL_VERSION_NUMBER < 0x10100000L
-        UNUSED(rc);
         alg_nid = OBJ_obj2nid(err_cert->cert_info->key->algor->algorithm);
 #else
         X509_PUBKEY *pubkey = X509_get_X509_PUBKEY(err_cert);
         ASN1_OBJECT *ppkalg = NULL;
-        rc = X509_PUBKEY_get0_param(&ppkalg, NULL, NULL, NULL, pubkey);
-        if (rc) {
+        if (X509_PUBKEY_get0_param(&ppkalg, NULL, NULL, NULL, pubkey)) {
             alg_nid = OBJ_obj2nid(ppkalg);
         }
 #endif
@@ -510,6 +539,18 @@ static int _tls_verify(int preverify_ok, X509_STORE_CTX *x509_ctx)
     return ret;
 }
 
+static int _tls_password_callback(char *buf, int size, int rwflag, void *u)
+{
+    xmpp_conn_t *conn = u;
+    UNUSED(rwflag);
+    if (!conn->password_callback) {
+        strophe_error(conn->ctx, "tls", "No password callback set");
+        return -1;
+    }
+    return conn->password_callback(buf, (size_t)size, conn->tls_client_key,
+                                   conn->password_callback_userdata);
+}
+
 tls_t *tls_new(xmpp_conn_t *conn)
 {
     tls_t *tls = strophe_alloc(conn->ctx, sizeof(*tls));
@@ -539,6 +580,8 @@ tls_t *tls_new(xmpp_conn_t *conn)
         SSL_CTX_set_options(tls->ssl_ctx, SSL_OP_NO_SSLv2); /* DROWN */
         SSL_CTX_set_options(tls->ssl_ctx, SSL_OP_NO_SSLv3); /* POODLE */
         SSL_CTX_set_options(tls->ssl_ctx, SSL_OP_NO_TLSv1); /* BEAST */
+        SSL_CTX_set_default_passwd_cb(tls->ssl_ctx, _tls_password_callback);
+        SSL_CTX_set_default_passwd_cb_userdata(tls->ssl_ctx, conn);
 
         if (conn->tls_client_cert && conn->tls_client_key) {
             tls->client_cert = _tls_cert_read(conn);
@@ -552,6 +595,21 @@ tls_t *tls_new(xmpp_conn_t *conn)
                                          SSL_FILETYPE_PEM);
             SSL_CTX_use_PrivateKey_file(tls->ssl_ctx, conn->tls_client_key,
                                         SSL_FILETYPE_PEM);
+        } else if (conn->tls_client_key) {
+            EVP_PKEY *pkey = NULL;
+            STACK_OF(X509) *ca = NULL;
+            X509 *cert = _tls_cert_read_p12(conn, &pkey, &ca);
+            if (!cert) {
+                goto err_free_ctx;
+            }
+
+            SSL_CTX_use_cert_and_key(tls->ssl_ctx, cert, pkey, ca, 1);
+
+            if (pkey)
+                EVP_PKEY_free(pkey);
+            if (ca)
+                sk_X509_pop_free(ca, X509_free);
+            tls->client_cert = cert;
         } else {
             /* If the server asks for a client certificate, don't send one. */
             SSL_CTX_set_client_cert_cb(tls->ssl_ctx, NULL);
@@ -848,7 +906,7 @@ static void _tls_dump_cert_info(tls_t *tls)
     }
 }
 
-static X509 *_tls_cert_read(xmpp_conn_t *conn)
+static X509 *_tls_cert_read_x509(xmpp_conn_t *conn)
 {
     if (conn->tls && conn->tls->client_cert)
         return conn->tls->client_cert;
@@ -865,6 +923,60 @@ static X509 *_tls_cert_read(xmpp_conn_t *conn)
     return c;
 }
 
+static X509 *
+_tls_cert_read_p12(xmpp_conn_t *conn, EVP_PKEY **pkey, STACK_OF(X509) * *ca)
+{
+    if (conn->tls && conn->tls->client_cert && !pkey && !ca)
+        return conn->tls->client_cert;
+    BIO *f = BIO_new_file(conn->tls_client_key, "r");
+    if (!f) {
+        strophe_debug(conn->ctx, "tls", "f == NULL");
+        goto error_out;
+    }
+    PKCS12 *p12 = d2i_PKCS12_bio(f, NULL);
+    BIO_free(f);
+    if (!p12) {
+        strophe_debug(conn->ctx, "tls", "Could not read p12 file");
+        goto error_out;
+    }
+
+    char pass[PEM_BUFSIZE];
+    int passlen = _tls_password_callback(pass, sizeof(pass), 0, conn);
+    if (passlen <= 0)
+        pass[0] = '\0';
+
+    /* For some reason `PKCS12_parse()` fails without a `EVP_PKEY`
+     * so if the user doesn't want it, use a local one and free it
+     * again directly after parsing.
+     */
+    EVP_PKEY *pkey_;
+    if (!pkey)
+        pkey = &pkey_;
+    X509 *cert = NULL;
+    int parse_ok = PKCS12_parse(p12, pass, pkey, &cert, ca);
+    if (pkey == &pkey_ && pkey_)
+        EVP_PKEY_free(pkey_);
+    PKCS12_free(p12);
+    if (!parse_ok) {
+        strophe_debug(conn->ctx, "tls", "Could not parse PKCS#12");
+        goto error_out;
+    }
+    return cert;
+error_out:
+    _tls_log_error(conn->ctx);
+    return NULL;
+}
+
+static X509 *_tls_cert_read(xmpp_conn_t *conn)
+{
+    if (conn->tls && conn->tls->client_cert)
+        return conn->tls->client_cert;
+    if (!conn->tls_client_cert && conn->tls_client_key) {
+        return _tls_cert_read_p12(conn, NULL, NULL);
+    }
+    return _tls_cert_read_x509(conn);
+}
+
 static int _tls_xaddr_nid(void)
 {
     static int xaddr_nid = NID_undef;
diff --git a/strophe.h b/strophe.h
index 7a5fe1c..69bd3b4 100644
--- a/strophe.h
+++ b/strophe.h
@@ -269,6 +269,39 @@ typedef void (*xmpp_conn_handler)(xmpp_conn_t *conn,
 typedef int (*xmpp_certfail_handler)(const xmpp_tlscert_t *cert,
                                      const char *const errormsg);
 
+/** The Handler function which will be called when the TLS stack can't
+ *  decrypt a password protected key file.
+ *
+ *  When this callback is called it shall write a NULL-terminated
+ *  string of maximum length `pw_max - 1` to `pw`.
+ *
+ *  This is currently only supported for GnuTLS and OpenSSL.
+ *
+ *  On 2022-02-02 the following maximum lengths are valid:
+ *  ```
+ *  include/gnutls/pkcs11.h: #define GNUTLS_PKCS11_MAX_PIN_LEN 256
+ *  include/openssl/pem.h: #define PEM_BUFSIZE 1024
+ *  ```
+ *
+ *  The usable length for GnuTLS is 255 as it expects a NULL-terminated string.
+ *
+ *  The usable length for OpenSSL is 1024.
+ *
+ *
+ *  @param pw       The buffer where the password shall be stored.
+ *  @param pw_max   The maximum length of the password.
+ *  @param fname    The name of the file that is going to be unlocked.
+ *  @param userdata The userdata pointer as supplied when setting this callback.
+ *
+ *  @return -1 on error, else the number of bytes written to `pw`
+ *
+ *  @ingroup TLS
+ */
+typedef int (*xmpp_password_callback)(char *pw,
+                                      size_t pw_max,
+                                      const char *fname,
+                                      void *userdata);
+
 /** The function which will be called when Strophe creates a new socket.
  *
  *  The `sock` argument is a pointer that is dependent on the architecture
@@ -319,6 +352,9 @@ void xmpp_conn_set_capath(xmpp_conn_t *const conn, const char *path);
 void xmpp_conn_set_certfail_handler(xmpp_conn_t *const conn,
                                     xmpp_certfail_handler hndl);
 xmpp_tlscert_t *xmpp_conn_get_peer_cert(xmpp_conn_t *const conn);
+void xmpp_conn_set_password_callback(xmpp_conn_t *conn,
+                                     xmpp_password_callback cb,
+                                     void *userdata);
 void xmpp_conn_set_client_cert(xmpp_conn_t *conn,
                                const char *cert,
                                const char *key);
diff --git a/tests/cert.pfx b/tests/cert.pfx
new file mode 100644
index 0000000..6d55fd8
Binary files /dev/null and b/tests/cert.pfx differ
diff --git a/tests/key_encrypted.pem b/tests/key_encrypted.pem
new file mode 100644
index 0000000..665185d
--- /dev/null
+++ b/tests/key_encrypted.pem
@@ -0,0 +1,8 @@
+-----BEGIN EC PRIVATE KEY-----
+Proc-Type: 4,ENCRYPTED
+DEK-Info: AES-256-CBC,30B7F2152A39184AEEF290ED2B1DBC0E
+
+IojJAF1hGHL9qnu5MCzl5l1PzsnxLj38JjLBLPXaNekiAbag5H9Tzr7y5nfyviPM
+hi6syrkXgLOBF+mZWJouOxCNx7+t6eWVfsDZcnzsw6HrTN/2xwkYP/3lYfzlnt6q
+/AKYQIUUPc/31J6xg3kGRQ==
+-----END EC PRIVATE KEY-----
diff --git a/tests/test.h b/tests/test.h
index 6166d5b..cd883a2 100644
--- a/tests/test.h
+++ b/tests/test.h
@@ -34,17 +34,17 @@
 #define ARRAY_SIZE(arr) (sizeof(arr) / sizeof((arr)[0]))
 #endif
 
-#define COMPARE(v1, v2)                         \
-    do {                                        \
-        const char *__v1 = v1;                  \
-        const char *__v2 = v2;                  \
-        if (strcmp(__v1, __v2) != 0) {          \
-            printf("Error:    %s\n"             \
-                   "Expected: %s\n"             \
-                   "Got:      %s\n",            \
-                   #v1 " != " #v2, __v1, __v2); \
-            exit(1);                            \
-        }                                       \
+#define COMPARE(v1, v2)                                  \
+    do {                                                 \
+        const char *__v1 = v1;                           \
+        const char *__v2 = v2;                           \
+        if (!__v1 || !__v2 || strcmp(__v1, __v2) != 0) { \
+            printf("Error:    %s\n"                      \
+                   "Expected: %s\n"                      \
+                   "Got:      %s\n",                     \
+                   #v1 " != " #v2, __v1, __v2);          \
+            exit(1);                                     \
+        }                                                \
     } while (0)
 
 #define COMPARE_BUF(v1, len1, v2, len2)                                \
diff --git a/tests/test_xmppaddr.c b/tests/test_xmppaddr.c
index 39539f9..b346f89 100644
--- a/tests/test_xmppaddr.c
+++ b/tests/test_xmppaddr.c
@@ -18,50 +18,71 @@
 
 #include "test.h"
 
+static int
+password_callback(char *pw, size_t pw_max, const char *fname, void *userdata)
+{
+    (void)pw_max;
+    (void)userdata;
+    (void)fname;
+    memcpy(pw, "abc123", 7);
+    return 6;
+}
+
 int main()
 {
     xmpp_ctx_t *ctx;
     xmpp_conn_t *conn;
     xmpp_log_t *log;
+    char *client_cert[][2] = {
+        {"tests/cert.pem", "tests/key.pem"},
+        {"tests/cert.pem", "tests/key_encrypted.pem"},
+        {NULL, "tests/cert.pfx"},
+    };
 
     char xmppaddr_num[] = "0";
-    unsigned int n;
+    unsigned int m, n;
 
     xmpp_initialize();
     log = xmpp_get_default_logger(XMPP_LEVEL_DEBUG);
     ctx = xmpp_ctx_new(NULL, log);
-    conn = xmpp_conn_new(ctx);
 
-    xmpp_conn_set_client_cert(conn, "tests/cert.pem", "tests/key.pem");
+    for (m = 0; m < sizeof(client_cert) / sizeof(client_cert[0]); ++m) {
+        conn = xmpp_conn_new(ctx);
 
-    xmppaddr_num[0] = xmppaddr_num[0] + xmpp_conn_cert_xmppaddr_num(conn);
+        xmpp_conn_set_password_callback(conn, password_callback, NULL);
 
-    COMPARE("2", xmppaddr_num);
+        xmpp_conn_set_client_cert(conn, client_cert[m][0], client_cert[m][1]);
 
-    for (n = 0; n < 3; ++n) {
-        char *r = xmpp_conn_cert_xmppaddr(conn, n);
-        switch (n) {
-        case 0:
-            COMPARE("very.long.username@so.the.asn1.length.is.a.valid.ascii."
+        xmppaddr_num[0] = '0' + xmpp_conn_cert_xmppaddr_num(conn);
+
+        COMPARE("2", xmppaddr_num);
+
+        for (n = 0; n < 3; ++n) {
+            char *r = xmpp_conn_cert_xmppaddr(conn, n);
+            switch (n) {
+            case 0:
+                COMPARE(
+                    "very.long.username@so.the.asn1.length.is.a.valid.ascii."
                     "character",
                     r);
-            break;
-        case 1:
-            COMPARE("second@xmpp.jid", r);
-            break;
-        default:
-            if (r != NULL) {
-                printf("\nThere shall only be two id-on-xmppAddr SANs!\nFound "
-                       "another one: %s\n",
-                       r);
-                exit(1);
+                break;
+            case 1:
+                COMPARE("second@xmpp.jid", r);
+                break;
+            default:
+                if (r != NULL) {
+                    printf("\nThere shall only be two id-on-xmppAddr SANs!\n"
+                           "Found another one: %s\n",
+                           r);
+                    exit(1);
+                }
+                break;
             }
-            break;
+            free(r);
         }
-        free(r);
+        xmpp_conn_release(conn);
     }
 
-    xmpp_conn_release(conn);
     xmpp_ctx_free(ctx);
     xmpp_shutdown();