Fix data race in RAND_DRBG_generate
[openssl.git] / crypto / rand / rand_lib.c
index 909f304..440c19c 100644 (file)
@@ -1,5 +1,5 @@
 /*
- * Copyright 1995-2017 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
  *
  * Licensed under the OpenSSL license (the "License").  You may not use
  * this file except in compliance with the License.  You can obtain a copy
@@ -15,6 +15,7 @@
 #include <openssl/engine.h>
 #include "internal/thread_once.h"
 #include "rand_lcl.h"
+#include "e_os.h"
 
 #ifndef OPENSSL_NO_ENGINE
 /* non-NULL if default_RAND_meth is ENGINE-provided */
@@ -24,9 +25,14 @@ static CRYPTO_RWLOCK *rand_engine_lock;
 static CRYPTO_RWLOCK *rand_meth_lock;
 static const RAND_METHOD *default_RAND_meth;
 static CRYPTO_ONCE rand_init = CRYPTO_ONCE_STATIC_INIT;
-RAND_BYTES_BUFFER rand_bytes;
+
 int rand_fork_count;
 
+static CRYPTO_RWLOCK *rand_nonce_lock;
+static int rand_nonce_count;
+
+static int rand_cleaning_up = 0;
+
 #ifdef OPENSSL_RAND_SEED_RDTSC
 /*
  * IMPORTANT NOTE:  It is not currently possible to use this code
@@ -37,12 +43,15 @@ int rand_fork_count;
 # error "RDTSC enabled?  Should not be possible!"
 
 /*
+ * Acquire entropy from high-speed clock
+ *
  * Since we get some randomness from the low-order bits of the
- * high-speec clock, it can help.  But don't return a status since
- * it's not sufficient to indicate whether or not the seeding was
- * done.
+ * high-speed clock, it can help.
+ *
+ * Returns the total entropy count, if it exceeds the requested
+ * entropy count. Otherwise, returns an entropy count of 0.
  */
-void rand_read_tsc(RAND_poll_cb rand_add, void *arg)
+size_t rand_acquire_entropy_from_tsc(RAND_POOL *pool)
 {
     unsigned char c;
     int i;
@@ -50,224 +59,649 @@ void rand_read_tsc(RAND_poll_cb rand_add, void *arg)
     if ((OPENSSL_ia32cap_P[0] & (1 << 4)) != 0) {
         for (i = 0; i < TSC_READ_COUNT; i++) {
             c = (unsigned char)(OPENSSL_rdtsc() & 0xFF);
-            rand_add(arg, &c, 1, 0.5);
+            rand_pool_add(pool, &c, 1, 4);
         }
     }
+    return rand_pool_entropy_available(pool);
 }
 #endif
 
 #ifdef OPENSSL_RAND_SEED_RDCPU
-size_t OPENSSL_ia32_rdseed_bytes(char *buf, size_t len);
-size_t OPENSSL_ia32_rdrand_bytes(char *buf, size_t len);
+size_t OPENSSL_ia32_rdseed_bytes(unsigned char *buf, size_t len);
+size_t OPENSSL_ia32_rdrand_bytes(unsigned char *buf, size_t len);
 
 extern unsigned int OPENSSL_ia32cap_P[];
 
-int rand_read_cpu(RAND_poll_cb rand_add, void *arg)
+/*
+ * Acquire entropy using Intel-specific cpu instructions
+ *
+ * Uses the RDSEED instruction if available, otherwise uses
+ * RDRAND if available.
+ *
+ * For the differences between RDSEED and RDRAND, and why RDSEED
+ * is the preferred choice, see https://goo.gl/oK3KcN
+ *
+ * Returns the total entropy count, if it exceeds the requested
+ * entropy count. Otherwise, returns an entropy count of 0.
+ */
+size_t rand_acquire_entropy_from_cpu(RAND_POOL *pool)
 {
-    char buff[RANDOMNESS_NEEDED];
-
-    /* If RDSEED is available, use that. */
-    if ((OPENSSL_ia32cap_P[2] & (1 << 18)) != 0) {
-        if (OPENSSL_ia32_rdseed_bytes(buff, sizeof(buff)) == sizeof(buff)) {
-            rand_add(arg, buff, (int)sizeof(buff), sizeof(buff));
-            return 1;
+    size_t bytes_needed;
+    unsigned char *buffer;
+
+    bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
+    if (bytes_needed > 0) {
+        buffer = rand_pool_add_begin(pool, bytes_needed);
+
+        if (buffer != NULL) {
+            /* Whichever comes first, use RDSEED, RDRAND or nothing */
+            if ((OPENSSL_ia32cap_P[2] & (1 << 18)) != 0) {
+                if (OPENSSL_ia32_rdseed_bytes(buffer, bytes_needed)
+                    == bytes_needed) {
+                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
+                }
+            } else if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
+                if (OPENSSL_ia32_rdrand_bytes(buffer, bytes_needed)
+                    == bytes_needed) {
+                    rand_pool_add_end(pool, bytes_needed, 8 * bytes_needed);
+                }
+            } else {
+                rand_pool_add_end(pool, 0, 0);
+            }
         }
     }
 
-    /* Second choice is RDRAND. */
-    if ((OPENSSL_ia32cap_P[1] & (1 << (62 - 32))) != 0) {
-        if (OPENSSL_ia32_rdrand_bytes(buff, sizeof(buff)) == sizeof(buff)) {
-            rand_add(arg, buff, (int)sizeof(buff), sizeof(buff));
-            return 1;
-        }
-    }
-
-    return 0;
+    return rand_pool_entropy_available(pool);
 }
 #endif
 
 
 /*
- * DRBG has two sets of callbacks; we only discuss the "entropy" one
- * here.  When the DRBG needs additional randomness bits (called entropy
- * in the NIST document), it calls the get_entropy callback which fills in
- * a pointer and returns the number of bytes. When the DRBG is finished with
- * the buffer, it calls the cleanup_entropy callback, with the value of
- * the buffer that the get_entropy callback filled in.
+ * Implements the get_entropy() callback (see RAND_DRBG_set_callbacks())
  *
- * Get entropy from the system, via RAND_poll if needed.  The |entropy|
- * is the bits of randomness required, and is expected to fit into a buffer
- * of |min_len|..|max__len| size.  We assume we're getting high-quality
- * randomness from the system, and that |min_len| bytes will do.
+ * If the DRBG has a parent, then the required amount of entropy input
+ * is fetched using the parent's RAND_DRBG_generate().
+ *
+ * Otherwise, the entropy is polled from the system entropy sources
+ * using rand_pool_acquire_entropy().
+ *
+ * If a random pool has been added to the DRBG using RAND_add(), then
+ * its entropy will be used up first.
  */
-size_t drbg_entropy_from_system(RAND_DRBG *drbg,
-                                unsigned char **pout,
-                                int entropy, size_t min_len, size_t max_len)
+size_t rand_drbg_get_entropy(RAND_DRBG *drbg,
+                             unsigned char **pout,
+                             int entropy, size_t min_len, size_t max_len,
+                             int prediction_resistance)
 {
-    int i;
-
-
-    if (min_len > (size_t)drbg->size) {
-        /* Should not happen.  See comment near RANDOMNESS_NEEDED. */
-        min_len = drbg->size;
+    size_t ret = 0;
+    size_t entropy_available = 0;
+    RAND_POOL *pool;
+
+    if (drbg->parent && drbg->strength > drbg->parent->strength) {
+        /*
+         * We currently don't support the algorithm from NIST SP 800-90C
+         * 10.1.2 to use a weaker DRBG as source
+         */
+        RANDerr(RAND_F_RAND_DRBG_GET_ENTROPY, RAND_R_PARENT_STRENGTH_TOO_WEAK);
+        return 0;
     }
 
-    if (drbg->filled) {
-        /* Re-use what we have. */
-        *pout = drbg->randomness;
-        return drbg->size;
+    if (drbg->pool != NULL) {
+        pool = drbg->pool;
+        pool->entropy_requested = entropy;
+    } else {
+        pool = rand_pool_new(entropy, min_len, max_len);
+        if (pool == NULL)
+            return 0;
     }
 
-    drbg->randomness = drbg->secure ? OPENSSL_secure_malloc(drbg->size)
-                                    : OPENSSL_malloc(drbg->size);
+    if (drbg->parent) {
+        size_t bytes_needed = rand_pool_bytes_needed(pool, 1 /*entropy_factor*/);
+        unsigned char *buffer = rand_pool_add_begin(pool, bytes_needed);
+
+        if (buffer != NULL) {
+            size_t bytes = 0;
+
+            /*
+             * Get random from parent, include our state as additional input.
+             * Our lock is already held, but we need to lock our parent before
+             * generating bits from it. (Note: taking the lock will be a no-op
+             * if locking if drbg->parent->lock == NULL.)
+             */
+            rand_drbg_lock(drbg->parent);
+            if (RAND_DRBG_generate(drbg->parent,
+                                   buffer, bytes_needed,
+                                   prediction_resistance,
+                                   NULL, 0) != 0)
+                bytes = bytes_needed;
+            drbg->reseed_next_counter
+                = tsan_load(&drbg->parent->reseed_prop_counter);
+            rand_drbg_unlock(drbg->parent);
+
+            rand_pool_add_end(pool, bytes, 8 * bytes);
+            entropy_available = rand_pool_entropy_available(pool);
+        }
+
+    } else {
+        if (prediction_resistance) {
+            /*
+             * We don't have any entropy sources that comply with the NIST
+             * standard to provide prediction resistance (see NIST SP 800-90C,
+             * Section 5.4).
+             */
+            RANDerr(RAND_F_RAND_DRBG_GET_ENTROPY,
+                    RAND_R_PREDICTION_RESISTANCE_NOT_SUPPORTED);
+            goto err;
+        }
 
-    /* If we don't have enough, try to get more. */
-    CRYPTO_THREAD_write_lock(rand_bytes.lock);
-    for (i = RAND_POLL_RETRIES; rand_bytes.curr < min_len && --i >= 0; ) {
-        CRYPTO_THREAD_unlock(rand_bytes.lock);
-        RAND_poll();
-        CRYPTO_THREAD_write_lock(rand_bytes.lock);
+        /* Get entropy by polling system entropy sources. */
+        entropy_available = rand_pool_acquire_entropy(pool);
     }
 
-    /* Get desired amount, but no more than we have. */
-    if (min_len > rand_bytes.curr)
-        min_len = rand_bytes.curr;
-    if (min_len != 0) {
-        memcpy(drbg->randomness, rand_bytes.buff, min_len);
-        drbg->filled = 1;
-        /* Update amount left and shift it down. */
-        rand_bytes.curr -= min_len;
-        if (rand_bytes.curr != 0)
-            memmove(rand_bytes.buff, &rand_bytes.buff[min_len], rand_bytes.curr);
+    if (entropy_available > 0) {
+        ret   = rand_pool_length(pool);
+        *pout = rand_pool_detach(pool);
     }
-    CRYPTO_THREAD_unlock(rand_bytes.lock);
-    *pout = drbg->randomness;
-    return min_len;
+
+ err:
+    /* we need to reset drbg->pool in the error case */
+    if (ret == 0 && drbg->pool != NULL)
+        drbg->pool = NULL;
+
+    rand_pool_free(pool);
+    return ret;
 }
 
-size_t drbg_entropy_from_parent(RAND_DRBG *drbg,
-                                unsigned char **pout,
-                                int entropy, size_t min_len, size_t max_len)
+/*
+ * Implements the cleanup_entropy() callback (see RAND_DRBG_set_callbacks())
+ *
+ */
+void rand_drbg_cleanup_entropy(RAND_DRBG *drbg,
+                               unsigned char *out, size_t outlen)
 {
-    int st;
+    if (drbg->pool == NULL)
+        OPENSSL_secure_clear_free(out, outlen);
+    else
+        drbg->pool = NULL;
+}
 
-    if (min_len > (size_t)drbg->size) {
-        /* Should not happen.  See comment near RANDOMNESS_NEEDED. */
-        min_len = drbg->size;
-    }
 
-    drbg->randomness = drbg->secure ? OPENSSL_secure_malloc(drbg->size)
-                                    : OPENSSL_malloc(drbg->size);
+/*
+ * Implements the get_nonce() callback (see RAND_DRBG_set_callbacks())
+ *
+ */
+size_t rand_drbg_get_nonce(RAND_DRBG *drbg,
+                           unsigned char **pout,
+                           int entropy, size_t min_len, size_t max_len)
+{
+    size_t ret = 0;
+    RAND_POOL *pool;
+
+    struct {
+        void * instance;
+        int count;
+    } data = { 0 };
 
-    /* Get random from parent, include our state as additional input. */
-    st = RAND_DRBG_generate(drbg->parent, drbg->randomness, min_len, 0,
-                            (unsigned char *)drbg, sizeof(*drbg));
-    if (st == 0)
+    pool = rand_pool_new(0, min_len, max_len);
+    if (pool == NULL)
         return 0;
-    drbg->filled = 1;
-    *pout = drbg->randomness;
-    return min_len;
+
+    if (rand_pool_add_nonce_data(pool) == 0)
+        goto err;
+
+    data.instance = drbg;
+    CRYPTO_atomic_add(&rand_nonce_count, 1, &data.count, rand_nonce_lock);
+
+    if (rand_pool_add(pool, (unsigned char *)&data, sizeof(data), 0) == 0)
+        goto err;
+
+    ret   = rand_pool_length(pool);
+    *pout = rand_pool_detach(pool);
+
+ err:
+    rand_pool_free(pool);
+
+    return ret;
 }
 
-void drbg_release_entropy(RAND_DRBG *drbg, unsigned char *out)
+/*
+ * Implements the cleanup_nonce() callback (see RAND_DRBG_set_callbacks())
+ *
+ */
+void rand_drbg_cleanup_nonce(RAND_DRBG *drbg,
+                             unsigned char *out, size_t outlen)
 {
-    drbg->filled = 0;
-    if (drbg->secure)
-        OPENSSL_secure_clear_free(drbg->randomness, drbg->size);
-    else
-        OPENSSL_clear_free(drbg->randomness, drbg->size);
-    drbg->randomness = NULL;
+    OPENSSL_secure_clear_free(out, outlen);
 }
 
-
 /*
- * Set up a global DRBG.
+ * Generate additional data that can be used for the drbg. The data does
+ * not need to contain entropy, but it's useful if it contains at least
+ * some bits that are unpredictable.
+ *
+ * Returns 0 on failure.
+ *
+ * On success it allocates a buffer at |*pout| and returns the length of
+ * the data. The buffer should get freed using OPENSSL_secure_clear_free().
  */
-static int setup_drbg(RAND_DRBG *drbg)
-{
-    int ret = 1;
-
-    drbg->lock = CRYPTO_THREAD_lock_new();
-    ret &= drbg->lock != NULL;
-    drbg->size = RANDOMNESS_NEEDED;
-    drbg->secure = CRYPTO_secure_malloc_initialized();
-    drbg->randomness = NULL;
-    /* If you change these parameters, see RANDOMNESS_NEEDED */
-    ret &= RAND_DRBG_set(drbg,
-                         NID_aes_128_ctr, RAND_DRBG_FLAG_CTR_USE_DF) == 1;
-    ret &= RAND_DRBG_set_callbacks(drbg, drbg_entropy_from_system,
-                                   drbg_release_entropy, NULL, NULL) == 1;
+size_t rand_drbg_get_additional_data(unsigned char **pout, size_t max_len)
+{
+    size_t ret = 0;
+    RAND_POOL *pool;
+
+    pool = rand_pool_new(0, 0, max_len);
+    if (pool == NULL)
+        return 0;
+
+    if (rand_pool_add_additional_data(pool) == 0)
+        goto err;
+
+    ret = rand_pool_length(pool);
+    *pout = rand_pool_detach(pool);
+
+ err:
+    rand_pool_free(pool);
+
     return ret;
 }
 
-static void free_drbg(RAND_DRBG *drbg)
+void rand_drbg_cleanup_additional_data(unsigned char *out, size_t outlen)
 {
-    CRYPTO_THREAD_lock_free(drbg->lock);
-    RAND_DRBG_uninstantiate(drbg);
+    OPENSSL_secure_clear_free(out, outlen);
 }
 
-void rand_fork()
+void rand_fork(void)
 {
     rand_fork_count++;
 }
 
 DEFINE_RUN_ONCE_STATIC(do_rand_init)
 {
-    int ret = 1;
-
 #ifndef OPENSSL_NO_ENGINE
     rand_engine_lock = CRYPTO_THREAD_lock_new();
-    ret &= rand_engine_lock != NULL;
+    if (rand_engine_lock == NULL)
+        return 0;
 #endif
+
     rand_meth_lock = CRYPTO_THREAD_lock_new();
-    ret &= rand_meth_lock != NULL;
-
-    rand_bytes.lock = CRYPTO_THREAD_lock_new();
-    ret &= rand_bytes.lock != NULL;
-    rand_bytes.curr = 0;
-    rand_bytes.size = MAX_RANDOMNESS_HELD;
-    rand_bytes.secure = CRYPTO_secure_malloc_initialized();
-    rand_bytes.buff = rand_bytes.secure
-        ? OPENSSL_secure_malloc(rand_bytes.size)
-        : OPENSSL_malloc(rand_bytes.size);
-    ret &= rand_bytes.buff != NULL;
-    ret &= setup_drbg(&rand_drbg);
-    ret &= setup_drbg(&priv_drbg);
-    return ret;
+    if (rand_meth_lock == NULL)
+        goto err1;
+
+    rand_nonce_lock = CRYPTO_THREAD_lock_new();
+    if (rand_nonce_lock == NULL)
+        goto err2;
+
+    if (!rand_cleaning_up && !rand_pool_init())
+        goto err3;
+
+    return 1;
+
+err3:
+    rand_pool_cleanup();
+err2:
+    CRYPTO_THREAD_lock_free(rand_meth_lock);
+    rand_meth_lock = NULL;
+err1:
+#ifndef OPENSSL_NO_ENGINE
+    CRYPTO_THREAD_lock_free(rand_engine_lock);
+    rand_engine_lock = NULL;
+#endif
+    return 0;
 }
 
 void rand_cleanup_int(void)
 {
     const RAND_METHOD *meth = default_RAND_meth;
 
+    rand_cleaning_up = 1;
+
     if (meth != NULL && meth->cleanup != NULL)
         meth->cleanup();
     RAND_set_rand_method(NULL);
+    rand_pool_cleanup();
 #ifndef OPENSSL_NO_ENGINE
     CRYPTO_THREAD_lock_free(rand_engine_lock);
+    rand_engine_lock = NULL;
 #endif
     CRYPTO_THREAD_lock_free(rand_meth_lock);
-    CRYPTO_THREAD_lock_free(rand_bytes.lock);
-    if (rand_bytes.secure)
-        OPENSSL_secure_clear_free(rand_bytes.buff, rand_bytes.size);
-    else
-        OPENSSL_clear_free(rand_bytes.buff, rand_bytes.size);
-    free_drbg(&rand_drbg);
-    free_drbg(&priv_drbg);
+    rand_meth_lock = NULL;
+    CRYPTO_THREAD_lock_free(rand_nonce_lock);
+    rand_nonce_lock = NULL;
 }
 
 /*
- * RAND_poll_ex() gets a function pointer to call when it has random bytes.
- * RAND_poll() sets the function pointer to be a wrapper that calls RAND_add().
+ * RAND_close_seed_files() ensures that any seed file decriptors are
+ * closed after use.
  */
-static void call_rand_add(void* arg, const void *buf, int num, double r)
+void RAND_keep_random_devices_open(int keep)
 {
-    RAND_add(buf, num, r);
+    rand_pool_keep_random_devices_open(keep);
 }
 
+/*
+ * RAND_poll() reseeds the default RNG using random input
+ *
+ * The random input is obtained from polling various entropy
+ * sources which depend on the operating system and are
+ * configurable via the --with-rand-seed configure option.
+ */
 int RAND_poll(void)
 {
-    return RAND_poll_ex(call_rand_add, NULL);
+    int ret = 0;
+
+    RAND_POOL *pool = NULL;
+
+    const RAND_METHOD *meth = RAND_get_rand_method();
+
+    if (meth == RAND_OpenSSL()) {
+        /* fill random pool and seed the master DRBG */
+        RAND_DRBG *drbg = RAND_DRBG_get0_master();
+
+        if (drbg == NULL)
+            return 0;
+
+        rand_drbg_lock(drbg);
+        ret = rand_drbg_restart(drbg, NULL, 0, 0);
+        rand_drbg_unlock(drbg);
+
+        return ret;
+
+    } else {
+        /* fill random pool and seed the current legacy RNG */
+        pool = rand_pool_new(RAND_DRBG_STRENGTH,
+                             RAND_DRBG_STRENGTH / 8,
+                             RAND_POOL_MAX_LENGTH);
+        if (pool == NULL)
+            return 0;
+
+        if (rand_pool_acquire_entropy(pool) == 0)
+            goto err;
+
+        if (meth->add == NULL
+            || meth->add(rand_pool_buffer(pool),
+                         rand_pool_length(pool),
+                         (rand_pool_entropy(pool) / 8.0)) == 0)
+            goto err;
+
+        ret = 1;
+    }
+
+err:
+    rand_pool_free(pool);
+    return ret;
+}
+
+/*
+ * Allocate memory and initialize a new random pool
+ */
+
+RAND_POOL *rand_pool_new(int entropy_requested, size_t min_len, size_t max_len)
+{
+    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));
+
+    if (pool == NULL) {
+        RANDerr(RAND_F_RAND_POOL_NEW, ERR_R_MALLOC_FAILURE);
+        return NULL;
+    }
+
+    pool->min_len = min_len;
+    pool->max_len = (max_len > RAND_POOL_MAX_LENGTH) ?
+        RAND_POOL_MAX_LENGTH : max_len;
+
+    pool->buffer = OPENSSL_secure_zalloc(pool->max_len);
+    if (pool->buffer == NULL) {
+        RANDerr(RAND_F_RAND_POOL_NEW, ERR_R_MALLOC_FAILURE);
+        goto err;
+    }
+
+    pool->entropy_requested = entropy_requested;
+
+    return pool;
+
+err:
+    OPENSSL_free(pool);
+    return NULL;
+}
+
+/*
+ * Attach new random pool to the given buffer
+ *
+ * This function is intended to be used only for feeding random data
+ * provided by RAND_add() and RAND_seed() into the <master> DRBG.
+ */
+RAND_POOL *rand_pool_attach(const unsigned char *buffer, size_t len,
+                            size_t entropy)
+{
+    RAND_POOL *pool = OPENSSL_zalloc(sizeof(*pool));
+
+    if (pool == NULL) {
+        RANDerr(RAND_F_RAND_POOL_ATTACH, ERR_R_MALLOC_FAILURE);
+        return NULL;
+    }
+
+    /*
+     * The const needs to be cast away, but attached buffers will not be
+     * modified (in contrary to allocated buffers which are zeroed and
+     * freed in the end).
+     */
+    pool->buffer = (unsigned char *) buffer;
+    pool->len = len;
+
+    pool->attached = 1;
+
+    pool->min_len = pool->max_len = pool->len;
+    pool->entropy = entropy;
+
+    return pool;
+}
+
+/*
+ * Free |pool|, securely erasing its buffer.
+ */
+void rand_pool_free(RAND_POOL *pool)
+{
+    if (pool == NULL)
+        return;
+
+    /*
+     * Although it would be advisable from a cryptographical viewpoint,
+     * we are not allowed to clear attached buffers, since they are passed
+     * to rand_pool_attach() as `const unsigned char*`.
+     * (see corresponding comment in rand_pool_attach()).
+     */
+    if (!pool->attached)
+        OPENSSL_secure_clear_free(pool->buffer, pool->max_len);
+    OPENSSL_free(pool);
+}
+
+/*
+ * Return the |pool|'s buffer to the caller (readonly).
+ */
+const unsigned char *rand_pool_buffer(RAND_POOL *pool)
+{
+    return pool->buffer;
+}
+
+/*
+ * Return the |pool|'s entropy to the caller.
+ */
+size_t rand_pool_entropy(RAND_POOL *pool)
+{
+    return pool->entropy;
+}
+
+/*
+ * Return the |pool|'s buffer length to the caller.
+ */
+size_t rand_pool_length(RAND_POOL *pool)
+{
+    return pool->len;
+}
+
+/*
+ * Detach the |pool| buffer and return it to the caller.
+ * It's the responsibility of the caller to free the buffer
+ * using OPENSSL_secure_clear_free().
+ */
+unsigned char *rand_pool_detach(RAND_POOL *pool)
+{
+    unsigned char *ret = pool->buffer;
+    pool->buffer = NULL;
+    return ret;
+}
+
+
+/*
+ * If |entropy_factor| bits contain 1 bit of entropy, how many bytes does one
+ * need to obtain at least |bits| bits of entropy?
+ */
+#define ENTROPY_TO_BYTES(bits, entropy_factor) \
+    (((bits) * (entropy_factor) + 7) / 8)
+
+
+/*
+ * Checks whether the |pool|'s entropy is available to the caller.
+ * This is the case when entropy count and buffer length are high enough.
+ * Returns
+ *
+ *  |entropy|  if the entropy count and buffer size is large enough
+ *      0      otherwise
+ */
+size_t rand_pool_entropy_available(RAND_POOL *pool)
+{
+    if (pool->entropy < pool->entropy_requested)
+        return 0;
+
+    if (pool->len < pool->min_len)
+        return 0;
+
+    return pool->entropy;
+}
+
+/*
+ * Returns the (remaining) amount of entropy needed to fill
+ * the random pool.
+ */
+
+size_t rand_pool_entropy_needed(RAND_POOL *pool)
+{
+    if (pool->entropy < pool->entropy_requested)
+        return pool->entropy_requested - pool->entropy;
+
+    return 0;
+}
+
+/*
+ * Returns the number of bytes needed to fill the pool, assuming
+ * the input has 1 / |entropy_factor| entropy bits per data bit.
+ * In case of an error, 0 is returned.
+ */
+
+size_t rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor)
+{
+    size_t bytes_needed;
+    size_t entropy_needed = rand_pool_entropy_needed(pool);
+
+    if (entropy_factor < 1) {
+        RANDerr(RAND_F_RAND_POOL_BYTES_NEEDED, RAND_R_ARGUMENT_OUT_OF_RANGE);
+        return 0;
+    }
+
+    bytes_needed = ENTROPY_TO_BYTES(entropy_needed, entropy_factor);
+
+    if (bytes_needed > pool->max_len - pool->len) {
+        /* not enough space left */
+        RANDerr(RAND_F_RAND_POOL_BYTES_NEEDED, RAND_R_RANDOM_POOL_OVERFLOW);
+        return 0;
+    }
+
+    if (pool->len < pool->min_len &&
+        bytes_needed < pool->min_len - pool->len)
+        /* to meet the min_len requirement */
+        bytes_needed = pool->min_len - pool->len;
+
+    return bytes_needed;
+}
+
+/* Returns the remaining number of bytes available */
+size_t rand_pool_bytes_remaining(RAND_POOL *pool)
+{
+    return pool->max_len - pool->len;
+}
+
+/*
+ * Add random bytes to the random pool.
+ *
+ * It is expected that the |buffer| contains |len| bytes of
+ * random input which contains at least |entropy| bits of
+ * randomness.
+ *
+ * Returns 1 if the added amount is adequate, otherwise 0
+ */
+int rand_pool_add(RAND_POOL *pool,
+                  const unsigned char *buffer, size_t len, size_t entropy)
+{
+    if (len > pool->max_len - pool->len) {
+        RANDerr(RAND_F_RAND_POOL_ADD, RAND_R_ENTROPY_INPUT_TOO_LONG);
+        return 0;
+    }
+
+    if (len > 0) {
+        memcpy(pool->buffer + pool->len, buffer, len);
+        pool->len += len;
+        pool->entropy += entropy;
+    }
+
+    return 1;
+}
+
+/*
+ * Start to add random bytes to the random pool in-place.
+ *
+ * Reserves the next |len| bytes for adding random bytes in-place
+ * and returns a pointer to the buffer.
+ * The caller is allowed to copy up to |len| bytes into the buffer.
+ * If |len| == 0 this is considered a no-op and a NULL pointer
+ * is returned without producing an error message.
+ *
+ * After updating the buffer, rand_pool_add_end() needs to be called
+ * to finish the udpate operation (see next comment).
+ */
+unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len)
+{
+    if (len == 0)
+        return NULL;
+
+    if (len > pool->max_len - pool->len) {
+        RANDerr(RAND_F_RAND_POOL_ADD_BEGIN, RAND_R_RANDOM_POOL_OVERFLOW);
+        return NULL;
+    }
+
+    return pool->buffer + pool->len;
+}
+
+/*
+ * Finish to add random bytes to the random pool in-place.
+ *
+ * Finishes an in-place update of the random pool started by
+ * rand_pool_add_begin() (see previous comment).
+ * It is expected that |len| bytes of random input have been added
+ * to the buffer which contain at least |entropy| bits of randomness.
+ * It is allowed to add less bytes than originally reserved.
+ */
+int rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy)
+{
+    if (len > pool->max_len - pool->len) {
+        RANDerr(RAND_F_RAND_POOL_ADD_END, RAND_R_RANDOM_POOL_OVERFLOW);
+        return 0;
+    }
+
+    if (len > 0) {
+        pool->len += len;
+        pool->entropy += entropy;
+    }
+
+    return 1;
 }
 
 int RAND_set_rand_method(const RAND_METHOD *meth)
@@ -365,15 +799,18 @@ void RAND_add(const void *buf, int num, double randomness)
 int RAND_priv_bytes(unsigned char *buf, int num)
 {
     const RAND_METHOD *meth = RAND_get_rand_method();
+    RAND_DRBG *drbg;
+    int ret;
 
     if (meth != RAND_OpenSSL())
         return RAND_bytes(buf, num);
 
-    if (priv_drbg.state == DRBG_UNINITIALISED
-            && RAND_DRBG_instantiate(&priv_drbg, NULL, 0) == 0)
+    drbg = RAND_DRBG_get0_private();
+    if (drbg == NULL)
         return 0;
-    return RAND_DRBG_generate(&priv_drbg, buf, num, 0, NULL, 0);
 
+    ret = RAND_DRBG_bytes(drbg, buf, num);
+    return ret;
 }
 
 int RAND_bytes(unsigned char *buf, int num)