Update to BearSSL 0.6+ release, add AES_CCM modes (#5164)

Pull in latest BearSSL head (0.6 + minor additions) release and add AES_CCM
modes to the encryption options. Enable the aes_ccm initialization in client/server

The EC mul20 and square20 code was identical in two different files,
but because these copies were static, we ended up with an extra 6k of
duplicated code. Updated BearSSL to make them shared, saving 6KB.

tools/sdk/include/bearssl/bearssl_rand.h

@@ -28,6 +28,9 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "bearssl_block.h"
+#include "bearssl_hash.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -93,6 +96,32 @@ extern "C" {
  * no currently known security penalty for exceeding the NIST limits,
  * and, in any case, HMAC_DRBG usage in implementing SSL/TLS always
  * stays much below these thresholds.
+ *
+ *
+ * ## AESCTR_DRBG
+ *
+ * AESCTR_DRBG is a custom PRNG based on AES-128 in CTR mode. This is
+ * meant to be used only in situations where you are desperate for
+ * speed, and have an hardware-optimized AES/CTR implementation. Whether
+ * this will yield perceptible improvements depends on what you use the
+ * pseudorandom bytes for, and how many you want; for instance, RSA key
+ * pair generation uses a substantial amount of randomness, and using
+ * AESCTR_DRBG instead of HMAC_DRBG yields a 15 to 20% increase in key
+ * generation speed on a recent x86 CPU (Intel Core i7-6567U at 3.30 GHz).
+ *
+ * Internally, it uses CTR mode with successive counter values, starting
+ * at zero (counter value expressed over 128 bits, big-endian convention).
+ * The counter is not allowed to reach 32768; thus, every 32768*16 bytes
+ * at most, the `update()` function is run (on an empty seed, if none is
+ * provided). The `update()` function computes the new AES-128 key by
+ * applying a custom hash function to the concatenation of a state-dependent
+ * word (encryption of an all-one block with the current key) and the new
+ * seed. The custom hash function uses Hirose's construction over AES-256;
+ * see the comments in `aesctr_drbg.c` for details.
+ *
+ * This DRBG does not follow an existing standard, and thus should be
+ * considered as inadequate for production use until it has been properly
+ * analysed.
  */
 
 /**
@@ -288,6 +317,79 @@ typedef int (*br_prng_seeder)(const br_prng_class **ctx);
  */
 br_prng_seeder br_prng_seeder_system(const char **name);
 
+/**
+ * \brief Context for AESCTR_DRBG.
+ *
+ * The context contents are opaque, except the first field, which
+ * supports OOP.
+ */
+typedef struct {
+	/**
+	 * \brief Pointer to the vtable.
+	 *
+	 * This field is set with the initialisation method/function.
+	 */
+	const br_prng_class *vtable;
+#ifndef BR_DOXYGEN_IGNORE
+	br_aes_gen_ctr_keys sk;
+	uint32_t cc;
+#endif
+} br_aesctr_drbg_context;
+
+/**
+ * \brief Statically allocated, constant vtable for AESCTR_DRBG.
+ */
+extern const br_prng_class br_aesctr_drbg_vtable;
+
+/**
+ * \brief AESCTR_DRBG initialisation.
+ *
+ * The context to initialise is provided as a pointer to its first field
+ * (the vtable pointer); this function sets that first field to a
+ * pointer to the vtable.
+ *
+ * The internal AES key is first set to the all-zero key; then, the
+ * `br_aesctr_drbg_update()` function is called with the provided `seed`.
+ * The call is performed even if the seed length (`seed_len`) is zero.
+ *
+ * The `aesctr` parameter defines the underlying AES/CTR implementation.
+ *
+ * \param ctx        AESCTR_DRBG context to initialise.
+ * \param aesctr     vtable for the AES/CTR implementation.
+ * \param seed       initial seed (can be `NULL` if `seed_len` is zero).
+ * \param seed_len   initial seed length (in bytes).
+ */
+void br_aesctr_drbg_init(br_aesctr_drbg_context *ctx,
+	const br_block_ctr_class *aesctr, const void *seed, size_t seed_len);
+
+/**
+ * \brief Random bytes generation with AESCTR_DRBG.
+ *
+ * This method produces `len` pseudorandom bytes, in the `out`
+ * buffer. The context is updated accordingly.
+ *
+ * \param ctx   AESCTR_DRBG context.
+ * \param out   output buffer.
+ * \param len   number of pseudorandom bytes to produce.
+ */
+void br_aesctr_drbg_generate(br_aesctr_drbg_context *ctx,
+	void *out, size_t len);
+
+/**
+ * \brief Inject additional seed bytes in AESCTR_DRBG.
+ *
+ * The provided seed bytes are added into the AESCTR_DRBG internal
+ * entropy pool. The process does not _replace_ existing entropy,
+ * thus pushing non-random bytes (i.e. bytes which are known to the
+ * attackers) does not degrade the overall quality of generated bytes.
+ *
+ * \param ctx        AESCTR_DRBG context.
+ * \param seed       additional seed.
+ * \param seed_len   additional seed length (in bytes).
+ */
+void br_aesctr_drbg_update(br_aesctr_drbg_context *ctx,
+	const void *seed, size_t seed_len);
+
 #ifdef __cplusplus
 }
 #endif