Index: Modules/_hashopenssl.c
===================================================================
--- Modules/_hashopenssl.c	(revision 82445)
+++ Modules/_hashopenssl.c	(working copy)
@@ -16,6 +16,9 @@
 #include "Python.h"
 #include "structmember.h"
 
+/* Provide the user with a way of finding out why a name isn't available */
+static PyObject *_errors_dict;
+
 #ifdef WITH_THREAD
 #include "pythread.h"
     #define ENTER_HASHLIB(obj) \
@@ -36,6 +39,8 @@
 #endif
 
 /* EVP is the preferred interface to hashing in OpenSSL */
+#include "openssl/ssl.h"
+#include "openssl/err.h"
 #include <openssl/evp.h>
 
 #define MUNCH_SIZE INT_MAX
@@ -525,11 +530,65 @@
     }
 
 /* used in the init function to setup a constructor */
-#define INIT_CONSTRUCTOR_CONSTANTS(NAME)  do { \
+static void
+hash_init_failure(PyObject *name)
+{
+    char buf[2048];
+    char *errstr;
+    PyObject *error_str;
+
+    errstr = ERR_error_string(ERR_peek_last_error(), NULL);
+    PyOS_snprintf(buf, sizeof(buf), "_hashopenssl.c:%d: %s", __LINE__, errstr);
+    ERR_clear_error();
+
+    error_str = PyString_FromString(buf);
+    if (!error_str)
+        return;
+
+    PyDict_SetItem(_errors_dict,
+                   name,
+                   error_str);
+}
+
+/* Remove a PyMethodDef from an arrary of them: */
+static int
+delete_method_by_name(struct PyMethodDef *ml, const char *name)
+{
+    assert(ml);
+    assert(name);
+
+    /* Find the def: */
+    while (ml->ml_name && strcmp(ml->ml_name, name)) {
+        ml++;
+    }
+    
+    if (!ml->ml_name) {
+      /* Not found */
+      return -1;
+    }
+
+    /* Delete this PyMethodDef by overwriting with the next defs until you
+       reach the sentinel value: */
+    *ml = ml[1];
+    while (ml->ml_name) {
+        ml++;
+        *ml = ml[1];
+    }
+
+    /* Success: */
+    return 0;
+}
+
+#define INIT_CONSTRUCTOR_CONSTANTS(NAME)  do {    \
     CONST_ ## NAME ## _name_obj = PyString_FromString(#NAME); \
     if (EVP_get_digestbyname(#NAME)) { \
         CONST_new_ ## NAME ## _ctx_p = &CONST_new_ ## NAME ## _ctx; \
-        EVP_DigestInit(CONST_new_ ## NAME ## _ctx_p, EVP_get_digestbyname(#NAME)); \
+        if (!EVP_DigestInit(CONST_new_ ## NAME ## _ctx_p, EVP_get_digestbyname(#NAME))) { \
+            /* Failure: */ \
+            hash_init_failure(CONST_ ## NAME ## _name_obj); \
+            CONST_new_ ## NAME ## _ctx_p = NULL; \
+            delete_method_by_name(EVP_functions, "openssl_" #NAME); \
+        } \
     } \
 } while (0);
 
@@ -565,13 +624,31 @@
 {
     PyObject *m;
 
+    _errors_dict = PyDict_New();
+    if (!_errors_dict)
+        return;
+    
+    SSL_load_error_strings();
+    SSL_library_init();
     OpenSSL_add_all_digests();
 
-    /* TODO build EVP_functions openssl_* entries dynamically based
-     * on what hashes are supported rather than listing many
-     * but having some be unsupported.  Only init appropriate
-     * constants. */
+    /* 
+       Figure out what hash functions are available, setting up the convenience
+       constructors, and removing those that aren't available from
+       the EVP_functions array.
 
+       Note: each method's generated PyCFunctionObject stores a copy of the
+       PyMethodDef*, so it's easiest to keep this as global data.
+    */
+    INIT_CONSTRUCTOR_CONSTANTS(md5);
+    INIT_CONSTRUCTOR_CONSTANTS(sha1);
+#ifdef _OPENSSL_SUPPORTS_SHA2
+    INIT_CONSTRUCTOR_CONSTANTS(sha224);
+    INIT_CONSTRUCTOR_CONSTANTS(sha256);
+    INIT_CONSTRUCTOR_CONSTANTS(sha384);
+    INIT_CONSTRUCTOR_CONSTANTS(sha512);
+#endif
+
     Py_TYPE(&EVPtype) = &PyType_Type;
     if (PyType_Ready(&EVPtype) < 0)
         return;
@@ -580,18 +657,11 @@
     if (m == NULL)
         return;
 
+    PyModule_AddObject(m, "_errors", _errors_dict);
+
 #if HASH_OBJ_CONSTRUCTOR
     Py_INCREF(&EVPtype);
     PyModule_AddObject(m, "HASH", (PyObject *)&EVPtype);
 #endif
 
-    /* these constants are used by the convenience constructors */
-    INIT_CONSTRUCTOR_CONSTANTS(md5);
-    INIT_CONSTRUCTOR_CONSTANTS(sha1);
-#ifdef _OPENSSL_SUPPORTS_SHA2
-    INIT_CONSTRUCTOR_CONSTANTS(sha224);
-    INIT_CONSTRUCTOR_CONSTANTS(sha256);
-    INIT_CONSTRUCTOR_CONSTANTS(sha384);
-    INIT_CONSTRUCTOR_CONSTANTS(sha512);
-#endif
 }