Seeded RNG: Add Jitter RNG entropy source

Signed-off-by: Stephan Mueller <smueller@chronox.de>

Author: smuellerDD

CHANGES.md

@@ -15,6 +15,8 @@ Changes 1.3.0-prerelease
 
 * ML-DSA: add external-mu support; new API: lc_dilithium_ctx_external_mu
 
+* Add optional Jitter RNG entropy source
+
 Changes 1.2.0
 * Locking für seeded_rng added to avoid requiring the caller providing a lock
 

README.fips.md

@@ -120,6 +120,8 @@ Leancrypto does not implement any entropy source. Yet, it implements support for
 
 * `esdm`: This option uses the [ESDM](http://chronox.de/esdm/index.html) as entropy source.
 
+* `jent`: This option uses the [Jitter RNG](http://chronox.de/jent/index.html) as entropy source.
+
 NOTE: The default RNG used by leancrypto is the XDRBG. At the time of writing (beginning 2025), it is not yet FIPS-approved. However, SP800-90A is subject to revision at the time of writing and it is planned to add the XDRBG as an approved algorithm. Therefore, leancrypto selects XDRBG as default. If that shall be changed, the macros `LC_SEEDED_RNG_CTX_SIZE` and `LC_SEEDED_RNG_CTX` found in `drng/src/seeded_rng.c` must be set to either the Hash DRBG or HMAC DRBG at compile time.
 
 ## API and Usage Documentation

drng/src/meson.build

@@ -86,6 +86,10 @@ if (seeded_rng == 1)
 		#Not required due to runtime linking
 		#leancrypto_link += cc.find_library( 'esdm_rpc_client',
 		#				    required: true)
+	elif get_option('seedsource') == 'jent'
+		src_fips += files([ 'seeded_rng_jent.c' ])
+		leancrypto_link += cc.find_library( 'jitterentropy',
+						    required: true)
 	elif (get_option('efi').enabled() or
 	      get_option('seedsource') == 'cpu')
 		src_fips += files([ 'seeded_rng_cpu.c' ])

drng/src/seeded_rng_jent.c

@@ -0,0 +1,89 @@
+/*
+ * ESDM Fast Entropy Source: Jitter RNG
+ *
+ * Copyright (C) 2022 - 2024, Stephan Mueller <smueller@chronox.de>
+ *
+ * License: see LICENSE file in root directory
+ *
+ * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF
+ * WHICH ARE HEREBY DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
+ * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+ * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
+ * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ */
+
+#include <jitterentropy.h>
+
+#include "fips_mode.h"
+#include "seeded_rng.h"
+#include "seeded_rng_linux.h"
+#include "ret_checkers.h"
+#include "visibility.h"
+
+static struct rand_data *esdm_jent_state = NULL;
+
+void seeded_rng_noise_fini(void)
+{
+	if (!esdm_jent_state)
+		return;
+
+	jent_entropy_collector_free(esdm_jent_state);
+	esdm_jent_state = NULL;
+}
+
+int seeded_rng_noise_init(void)
+{
+	unsigned int flags = 0;
+	int ret;
+
+	/* Allow the init function to be called multiple times */
+	seeded_rng_noise_fini();
+
+	flags |= fips140_mode_enabled() ? JENT_FORCE_FIPS : 0;
+
+	CKINT(jent_entropy_init_ex(0, flags));
+
+	esdm_jent_state = jent_entropy_collector_alloc(0, flags);
+	CKNULL(esdm_jent_state, -EFAULT);
+
+out:
+	return ret;
+}
+
+ssize_t get_full_entropy(uint8_t *buffer, size_t bufferlen)
+{
+	ssize_t ret;
+
+	ret = jent_read_entropy_safe(&esdm_jent_state, (char *)buffer,
+				     bufferlen);
+
+	switch (ret) {
+	case -1:
+		ret = -EOPNOTSUPP;
+		break;
+	/* Temporary errors */
+	case -2:
+	case -3:
+	case -5:
+		ret = -ENODATA;
+		break;
+	/* Permanent errors */
+	case -6:
+	case -7:
+	case -8:
+	case -4:
+		ret = -EFAULT;
+		break;
+	default:
+		break;
+	}
+
+	return ret;
+}

meson_options.txt

@@ -178,6 +178,7 @@ option('seedsource', type: 'combo', value: 'builtin',
 	choices: ['builtin',
 		  'cpu',
 		  'esdm',
+		  'jent',
 		 ],
 	description: '''Select the seed source for leancrypto