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Diffstat (limited to '')
-rw-r--r-- | c/src/lib/libbsp/shared/getentropy-cpucounter.c | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/c/src/lib/libbsp/shared/getentropy-cpucounter.c b/c/src/lib/libbsp/shared/getentropy-cpucounter.c new file mode 100644 index 0000000000..15c8648047 --- /dev/null +++ b/c/src/lib/libbsp/shared/getentropy-cpucounter.c @@ -0,0 +1,54 @@ +/* + * Copyright (c) 2017 embedded brains GmbH. All rights reserved. + * + * embedded brains GmbH + * Dornierstr. 4 + * 82178 Puchheim + * Germany + * <rtems@embedded-brains.de> + * + * The license and distribution terms for this file may be + * found in the file LICENSE in this distribution or at + * http://www.rtems.org/license/LICENSE. + */ + +/* + * ATTENTION: THIS IS A VERY LIMITED ENTROPY SOURCE. + * + * This implementation uses a time-based value for it's entropy. The only thing + * that makes it random are interrupts from external sources. Don't use it if + * you need for example a strong crypto. + */ + +#include <unistd.h> +#include <string.h> +#include <rtems/sysinit.h> +#include <rtems/counter.h> + +int getentropy(void *ptr, size_t n) +{ + uint8_t *dest = ptr; + + while (n > 0) { + rtems_counter_ticks ticks; + + ticks = rtems_counter_read(); + + if (n >= sizeof(ticks)) { + memcpy(dest, &ticks, sizeof(ticks)); + n -= sizeof(ticks); + dest += sizeof(ticks); + } else { + /* + * Fill the remaining bytes with only the least + * significant byte of the time. That is the byte with + * the most changes. + */ + *dest = ticks & 0xFF; + --n; + ++dest; + } + } + + return 0; +} |