diff --git a/include/qpdf/QPDFCryptoProvider.hh b/include/qpdf/QPDFCryptoProvider.hh
index 4243fcfd..eb5dcf34 100644
--- a/include/qpdf/QPDFCryptoProvider.hh
+++ b/include/qpdf/QPDFCryptoProvider.hh
@@ -26,6 +26,7 @@
 #include <qpdf/QPDFCryptoImpl.hh>
 #include <string>
 #include <map>
+#include <set>
 #include <memory>
 #include <functional>
 
@@ -64,6 +65,14 @@ class QPDFCryptoProvider
     QPDF_DLL
     static void setDefaultProvider(std::string const& name);
 
+    // Get the names of registered implementations
+    QPDF_DLL
+    static std::set<std::string> getRegisteredImpls();
+
+    // Get the name of the default crypto provider
+    QPDF_DLL
+    static std::string getDefaultProvider();
+
   private:
     QPDFCryptoProvider();
     ~QPDFCryptoProvider() = default;
diff --git a/libqpdf/QPDFCryptoProvider.cc b/libqpdf/QPDFCryptoProvider.cc
index 133a16f7..5755fcca 100644
--- a/libqpdf/QPDFCryptoProvider.cc
+++ b/libqpdf/QPDFCryptoProvider.cc
@@ -1,5 +1,6 @@
 #include <qpdf/QPDFCryptoProvider.hh>
 #include <qpdf/qpdf-config.h>
+#include <qpdf/QUtil.hh>
 #include <stdexcept>
 
 #ifdef USE_CRYPTO_NATIVE
@@ -49,7 +50,12 @@ QPDFCryptoProvider::QPDFCryptoProvider() :
 #ifdef USE_CRYPTO_GNUTLS
     registerImpl_internal<QPDFCrypto_gnutls>("gnutls");
 #endif
-    setDefaultProvider_internal(DEFAULT_CRYPTO);
+    std::string default_crypto;
+    if (! QUtil::get_env("QPDF_CRYPTO_PROVIDER", &default_crypto))
+    {
+        default_crypto = DEFAULT_CRYPTO;
+    }
+    setDefaultProvider_internal(default_crypto);
 }
 
 QPDFCryptoProvider&
@@ -83,5 +89,31 @@ QPDFCryptoProvider::registerImpl_internal(std::string const& name)
 void
 QPDFCryptoProvider::setDefaultProvider_internal(std::string const& name)
 {
+    if (! this->m->providers.count(name))
+    {
+        throw std::logic_error(
+            "QPDFCryptoProvider: request to set default"
+            " provider to unknown implementation \"" +
+            name + "\"");
+    }
     this->m->default_provider = name;
 }
+
+std::set<std::string>
+QPDFCryptoProvider::getRegisteredImpls()
+{
+    std::set<std::string> result;
+    QPDFCryptoProvider& p = getInstance();
+    for (auto iter = p.m->providers.begin(); iter != p.m->providers.end();
+         ++iter)
+    {
+        result.insert((*iter).first);
+    }
+    return result;
+}
+
+std::string
+QPDFCryptoProvider::getDefaultProvider()
+{
+    return getInstance().m->default_provider;
+}
diff --git a/qpdf/qpdf.cc b/qpdf/qpdf.cc
index 3f23420d..2bd98ccb 100644
--- a/qpdf/qpdf.cc
+++ b/qpdf/qpdf.cc
@@ -24,6 +24,7 @@
 #include <qpdf/QPDFAcroFormDocumentHelper.hh>
 #include <qpdf/QPDFExc.hh>
 #include <qpdf/QPDFSystemError.hh>
+#include <qpdf/QPDFCryptoProvider.hh>
 
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QIntC.hh>
@@ -624,6 +625,7 @@ class ArgParser
     void argCompletionBash();
     void argCompletionZsh();
     void argJsonHelp();
+    void argShowCrypto();
     void argPositional(char* arg);
     void argPassword(char* parameter);
     void argEmpty();
@@ -829,6 +831,7 @@ ArgParser::initOptionTable()
     (*t)["completion-bash"] = oe_bare(&ArgParser::argCompletionBash);
     (*t)["completion-zsh"] = oe_bare(&ArgParser::argCompletionZsh);
     (*t)["json-help"] = oe_bare(&ArgParser::argJsonHelp);
+    (*t)["show-crypto"] = oe_bare(&ArgParser::argShowCrypto);
 
     t = &this->main_option_table;
     char const* yn[] = {"y", "n", 0};
@@ -1098,6 +1101,7 @@ ArgParser::argHelp()
         << "--version               show version of qpdf\n"
         << "--copyright             show qpdf's copyright and license information\n"
         << "--help                  show command-line argument help\n"
+        << "--show-crypto           show supported crypto providers; default is first\n"
         << "--completion-bash       output a bash complete command you can eval\n"
         << "--completion-zsh        output a zsh complete command you can eval\n"
         << "--password=password     specify a password for accessing encrypted files\n"
@@ -1551,6 +1555,21 @@ ArgParser::argJsonHelp()
         << std::endl;
 }
 
+void
+ArgParser::argShowCrypto()
+{
+    auto crypto = QPDFCryptoProvider::getRegisteredImpls();
+    std::string default_crypto = QPDFCryptoProvider::getDefaultProvider();
+    std::cout << default_crypto << std::endl;
+    for (auto iter = crypto.begin(); iter != crypto.end(); ++iter)
+    {
+        if (*iter != default_crypto)
+        {
+            std::cout << *iter << std::endl;
+        }
+    }
+}
+
 void
 ArgParser::argPassword(char* parameter)
 {
@@ -5228,10 +5247,10 @@ int realmain(int argc, char* argv[])
     // it holds dynamic memory used for argv.
     Options o;
     ArgParser ap(argc, argv, o);
-    ap.parseOptions();
 
     try
     {
+        ap.parseOptions();
 	PointerHolder<QPDF> pdf_ph =
             process_file(o.infilename, o.password, o);
         QPDF& pdf = *pdf_ph;