--- /dev/null
+/*
+ * Copyright 1995-2020 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
+ */
+
+#ifndef OSSL_PROVIDER_RAND_POOL_H
+# define OSSL_PROVIDER_RAND_POOL_H
+
+# include <stdio.h>
+# include <openssl/rand_drbg.h>
+
+/*
+ * Maximum allocation size for RANDOM_POOL buffers
+ *
+ * The max_len value for the buffer provided to the rand_drbg_get_entropy()
+ * callback is currently 2^31 bytes (2 gigabytes), if a derivation function
+ * is used. Since this is much too large to be allocated, the rand_pool_new()
+ * function chooses more modest values as default pool length, bounded
+ * by RAND_POOL_MIN_LENGTH and RAND_POOL_MAX_LENGTH
+ *
+ * The choice of the RAND_POOL_FACTOR is large enough such that the
+ * RAND_POOL can store a random input which has a lousy entropy rate of
+ * 8/256 (= 0.03125) bits per byte. This input will be sent through the
+ * derivation function which 'compresses' the low quality input into a
+ * high quality output.
+ *
+ * The factor 1.5 below is the pessimistic estimate for the extra amount
+ * of entropy required when no get_nonce() callback is defined.
+ */
+# define RAND_POOL_FACTOR 256
+# define RAND_POOL_MAX_LENGTH (RAND_POOL_FACTOR * \
+ 3 * (RAND_DRBG_STRENGTH / 16))
+/*
+ * = (RAND_POOL_FACTOR * \
+ * 1.5 * (RAND_DRBG_STRENGTH / 8))
+ */
+
+/*
+ * Initial allocation minimum.
+ *
+ * There is a distinction between the secure and normal allocation minimums.
+ * Ideally, the secure allocation size should be a power of two. The normal
+ * allocation size doesn't have any such restriction.
+ *
+ * The secure value is based on 128 bits of secure material, which is 16 bytes.
+ * Typically, the DRBGs will set a minimum larger than this so optimal
+ * allocation ought to take place (for full quality seed material).
+ *
+ * The normal value has been chosen by noticing that the rand_drbg_get_nonce
+ * function is usually the largest of the built in allocation (twenty four
+ * bytes and then appending another sixteen bytes). This means the buffer ends
+ * with 40 bytes. The value of forty eight is comfortably above this which
+ * allows some slack in the platform specific values used.
+ */
+# define RAND_POOL_MIN_ALLOCATION(secure) ((secure) ? 16 : 48)
+
+/*
+ * The 'random pool' acts as a dumb container for collecting random
+ * input from various entropy sources. It is the callers duty to 1) initialize
+ * the random pool, 2) pass it to the polling callbacks, 3) seed the RNG, and
+ * 4) cleanup the random pool again.
+ *
+ * The random pool contains no locking mechanism because its scope and
+ * lifetime is intended to be restricted to a single stack frame.
+ */
+typedef struct rand_pool_st {
+ unsigned char *buffer; /* points to the beginning of the random pool */
+ size_t len; /* current number of random bytes contained in the pool */
+
+ int attached; /* true pool was attached to existing buffer */
+ int secure; /* 1: allocated on the secure heap, 0: otherwise */
+
+ size_t min_len; /* minimum number of random bytes requested */
+ size_t max_len; /* maximum number of random bytes (allocated buffer size) */
+ size_t alloc_len; /* current number of bytes allocated */
+ size_t entropy; /* current entropy count in bits */
+ size_t entropy_requested; /* requested entropy count in bits */
+} RAND_POOL;
+
+RAND_POOL *rand_pool_new(int entropy_requested, int secure,
+ size_t min_len, size_t max_len);
+RAND_POOL *rand_pool_attach(const unsigned char *buffer, size_t len,
+ size_t entropy);
+void rand_pool_free(RAND_POOL *pool);
+
+const unsigned char *rand_pool_buffer(RAND_POOL *pool);
+unsigned char *rand_pool_detach(RAND_POOL *pool);
+void rand_pool_reattach(RAND_POOL *pool, unsigned char *buffer);
+
+size_t rand_pool_entropy(RAND_POOL *pool);
+size_t rand_pool_length(RAND_POOL *pool);
+
+size_t rand_pool_entropy_available(RAND_POOL *pool);
+size_t rand_pool_entropy_needed(RAND_POOL *pool);
+/* |entropy_factor| expresses how many bits of data contain 1 bit of entropy */
+size_t rand_pool_bytes_needed(RAND_POOL *pool, unsigned int entropy_factor);
+size_t rand_pool_bytes_remaining(RAND_POOL *pool);
+
+int rand_pool_add(RAND_POOL *pool,
+ const unsigned char *buffer, size_t len, size_t entropy);
+unsigned char *rand_pool_add_begin(RAND_POOL *pool, size_t len);
+int rand_pool_add_end(RAND_POOL *pool, size_t len, size_t entropy);
+
+#endif /* OSSL_PROVIDER_RAND_POOL_H */
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