rand_drbg: remove RAND_DRBG.

The RAND_DRBG API did not fit well into the new provider concept as
implemented by EVP_RAND and EVP_RAND_CTX. The main reason is that the
RAND_DRBG API is a mixture of 'front end' and 'back end' API calls
and some of its API calls are rather low-level. This holds in particular
for the callback mechanism (RAND_DRBG_set_callbacks()) and the RAND_DRBG
type changing mechanism (RAND_DRBG_set()).

Adding a compatibility layer to continue supporting the RAND_DRBG API as
a legacy API for a regular deprecation period turned out to come at the
price of complicating the new provider API unnecessarily. Since the
RAND_DRBG API exists only since version 1.1.1, it was decided by the OMC
to drop it entirely.

Other related changes:

Use RNG instead of DRBG in EVP_RAND documentation.  The documentation was
using DRBG in places where it should have been RNG or CSRNG.

Move the RAND_DRBG(7) documentation to EVP_RAND(7).

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/12509)

1 files changed, 69 insertions, 0 deletions

diff --git a/crypto/rand/rand_meth.c b/crypto/rand/rand_meth.c
new file mode 100644
index 0000000..e9237a4
--- /dev/null
+++ b/crypto/rand/rand_meth.c
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2011-2020 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License 2.0 (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include <openssl/evp.h>
+#include <openssl/rand.h>
+#include "rand_local.h"
+
+/* Implements the default OpenSSL RAND_add() method */
+static int drbg_add(const void *buf, int num, double randomness)
+{
+    EVP_RAND_CTX *drbg = RAND_get0_primary(NULL);
+
+    if (drbg == NULL || num <= 0)
+        return 0;
+
+    return EVP_RAND_reseed(drbg, 0, NULL, 0, buf, num);
+}
+
+/* Implements the default OpenSSL RAND_seed() method */
+static int drbg_seed(const void *buf, int num)
+{
+    return drbg_add(buf, num, num);
+}
+
+/* Implements the default OpenSSL RAND_status() method */
+static int drbg_status(void)
+{
+    EVP_RAND_CTX *drbg = RAND_get0_primary(NULL);
+
+    if (drbg == NULL)
+        return 0;
+
+    return  EVP_RAND_state(drbg) == EVP_RAND_STATE_READY ? 1 : 0;
+}
+
+/* Implements the default OpenSSL RAND_bytes() method */
+static int drbg_bytes(unsigned char *out, int count)
+{
+    EVP_RAND_CTX *drbg = RAND_get0_public(NULL);
+
+    if (drbg == NULL)
+        return 0;
+
+    return EVP_RAND_generate(drbg, out, count, 0, 0, NULL, 0);
+}
+
+RAND_METHOD rand_meth = {
+    drbg_seed,
+    drbg_bytes,
+    NULL,
+    drbg_add,
+    drbg_bytes,
+    drbg_status
+};
+
+RAND_METHOD *RAND_OpenSSL(void)
+{
+#ifndef FIPS_MODULE
+    return &rand_meth;
+#else
+    return NULL;
+#endif
+}