/* * PRNG: Pseudo Random Number Generator * Based on NIST Recommended PRNG From ANSI X9.31 Appendix A.2.4 using * AES 128 cipher * * (C) Neil Horman <nhorman@tuxdriver.com> * * This program is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License as published by the * Free Software Foundation; either version 2 of the License, or (at your * any later version. * * */ #include <crypto/internal/rng.h> #include <linux/err.h> #include <linux/init.h> #include <linux/module.h> #include <linux/moduleparam.h> #include <linux/string.h> #include "internal.h" #define DEFAULT_PRNG_KEY "0123456789abcdef" #define DEFAULT_PRNG_KSZ 16 #define DEFAULT_BLK_SZ 16 #define DEFAULT_V_SEED "zaybxcwdveuftgsh" /* * Flags for the prng_context flags field */ #define PRNG_FIXED_SIZE 0x1 #define PRNG_NEED_RESET 0x2 /* * Note: DT is our counter value * I is our intermediate value * V is our seed vector * See http://csrc.nist.gov/groups/STM/cavp/documents/rng/931rngext.pdf * for implementation details */ struct prng_context { spinlock_t prng_lock; unsigned char rand_data[DEFAULT_BLK_SZ]; unsigned char last_rand_data[DEFAULT_BLK_SZ]; unsigned char DT[DEFAULT_BLK_SZ]; unsigned char I[DEFAULT_BLK_SZ]; unsigned char V[DEFAULT_BLK_SZ]; u32 rand_data_valid; struct crypto_cipher *tfm; u32 flags; }; static int dbg; static void hexdump(char *note, unsigned char *buf, unsigned int len) { if (dbg) { printk(KERN_CRIT "%s", note); print_hex_dump(KERN_CONT, "", DUMP_PREFIX_OFFSET, 16, 1, buf, len, false); } } #define dbgprint(format, args...) do {\ if (dbg)\ printk(format, ##args);\ } while (0) static void xor_vectors(unsigned char *in1, unsigned char *in2, unsigned char *out, unsigned int size) { int i; for (i = 0; i < size; i++) out[i] = in1[i] ^ in2[i]; } /* * Returns DEFAULT_BLK_SZ bytes of random data per call * returns 0 if generation succeded, <0 if something went wrong */ static int _get_more_prng_bytes(struct prng_context *ctx) { int i; unsigned char tmp[DEFAULT_BLK_SZ]; unsigned char *output = NULL; dbgprint(KERN_CRIT "Calling _get_more_prng_bytes for context %p\n", ctx); hexdump("Input DT: ", ctx->DT, DEFAULT_BLK_SZ); hexdump("Input I: ", ctx->I, DEFAULT_BLK_SZ); hexdump("Input V: ", ctx->V, DEFAULT_BLK_SZ); /* * This algorithm is a 3 stage state machine */ for (i = 0; i < 3; i++) { switch (i) { case 0: /* * Start by encrypting the counter value * This gives us an intermediate value I */ memcpy(tmp, ctx->DT, DEFAULT_BLK_SZ); output = ctx->I; hexdump("tmp stage 0: ", tmp, DEFAULT_BLK_SZ); break; case 1: /* * Next xor I with our secret vector V * encrypt that result to obtain our * pseudo random data which we output */ xor_vectors(ctx->I, ctx->V, tmp, DEFAULT_BLK_SZ); hexdump("tmp stage 1: ", tmp, DEFAULT_BLK_SZ); output = ctx->rand_data; break; case 2: /* * First check that we didn't produce the same * random data that we did last time around through this */ if (!memcmp(ctx->rand_data, ctx->last_rand_data, DEFAULT_BLK_SZ)) { if (fips_enabled) { panic("cprng %p Failed repetition check!\n", ctx); } printk(KERN_ERR "ctx %p Failed repetition check!\n", ctx); ctx->flags |= PRNG_NEED_RESET; return -EINVAL; } memcpy(ctx->last_rand_data, ctx->rand_data, DEFAULT_BLK_SZ); /* * Lastly xor the random data with I * and encrypt that to obtain a new secret vector V */ xor_vectors(ctx->rand_data, ctx->I, tmp, DEFAULT_BLK_SZ); output = ctx->V; hexdump("tmp stage 2: ", tmp, DEFAULT_BLK_SZ); break; } /* do the encryption */ crypto_cipher_encrypt_one(ctx->tfm, output, tmp); } /* * Now update our DT value */ for (i = DEFAULT_BLK_SZ - 1; i >= 0; i--) { ctx->DT[i] += 1; if (ctx->DT[i] != 0) break; } dbgprint("Returning new block for context %p\n", ctx); ctx->rand_data_valid = 0; hexdump("Output DT: ", ctx->DT, DEFAULT_BLK_SZ); hexdump("Output I: ", ctx->I, DEFAULT_BLK_SZ); hexdump("Output V: ", ctx->V, DEFAULT_BLK_SZ); hexdump("New Random Data: ", ctx->rand_data, DEFAULT_BLK_SZ); return 0; } /* Our exported functions */ static int get_prng_bytes(char *buf, size_t nbytes, struct prng_context *ctx) { unsigned char *ptr = buf; unsigned int byte_count = (unsigned int)nbytes; int err; if (nbytes < 0) return -EINVAL; spin_lock_bh(&ctx->prng_lock); err = -EINVAL; if (ctx->flags & PRNG_NEED_RESET) goto done; /* * If the FIXED_SIZE flag is on, only return whole blocks of * pseudo random data */ err = -EINVAL; if (ctx->flags & PRNG_FIXED_SIZE) { if (nbytes < DEFAULT_BLK_SZ) goto done; byte_count = DEFAULT_BLK_SZ; } err = byte_count; dbgprint(KERN_CRIT "getting %d random bytes for context %p\n", byte_count, ctx); remainder: if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { if (_get_more_prng_bytes(ctx) < 0) { memset(buf, 0, nbytes); err = -EINVAL; goto done; } } /* * Copy any data less than an entire block */ if (byte_count < DEFAULT_BLK_SZ) { empty_rbuf: for (; ctx->rand_data_valid < DEFAULT_BLK_SZ; ctx->rand_data_valid++) { *ptr = ctx->rand_data[ctx->rand_data_valid]; ptr++; byte_count--; if (byte_count == 0) goto done; } } /* * Now copy whole blocks */ for (; byte_count >= DEFAULT_BLK_SZ; byte_count -= DEFAULT_BLK_SZ) { if (ctx->rand_data_valid == DEFAULT_BLK_SZ) { if (_get_more_prng_bytes(ctx) < 0) { memset(buf, 0, nbytes); err = -EINVAL; goto done; } } if (ctx->rand_data_valid > 0) goto empty_rbuf; memcpy(ptr, ctx->rand_data, DEFAULT_BLK_SZ); ctx->rand_data_valid += DEFAULT_BLK_SZ; ptr += DEFAULT_BLK_SZ; } /* * Now go back and get any remaining partial block */ if (byte_count) goto remainder; done: spin_unlock_bh(&ctx->prng_lock); dbgprint(KERN_CRIT "returning %d from get_prng_bytes in context %p\n", err, ctx); return err; } static void free_prng_context(struct prng_context *ctx) { crypto_free_cipher(ctx->tfm); } static int reset_prng_context(struct prng_context *ctx, unsigned char *key, size_t klen, unsigned char *V, unsigned char *DT) { int ret; unsigned char *prng_key; spin_lock_bh(&ctx->prng_lock); ctx->flags |= PRNG_NEED_RESET; prng_key = (key != NULL) ? key : (unsigned char *)DEFAULT_PRNG_KEY; if (!key) klen = DEFAULT_PRNG_KSZ; if (V) memcpy(ctx->V, V, DEFAULT_BLK_SZ); else memcpy(ctx->V, DEFAULT_V_SEED, DEFAULT_BLK_SZ); if (DT) memcpy(ctx->DT, DT, DEFAULT_BLK_SZ); else memset(ctx->DT, 0, DEFAULT_BLK_SZ); memset(ctx->rand_data, 0, DEFAULT_BLK_SZ); memset(ctx->last_rand_data, 0, DEFAULT_BLK_SZ); ctx->rand_data_valid = DEFAULT_BLK_SZ; ret = crypto_cipher_setkey(ctx->tfm, prng_key, klen); if (ret) { dbgprint(KERN_CRIT "PRNG: setkey() failed flags=%x\n", crypto_cipher_get_flags(ctx->tfm)); goto out; } ret = 0; ctx->flags &= ~PRNG_NEED_RESET; out: spin_unlock_bh(&ctx->prng_lock); return ret; } static int cprng_init(struct crypto_tfm *tfm) { struct prng_context *ctx = crypto_tfm_ctx(tfm); spin_lock_init(&ctx->prng_lock); ctx->tfm = crypto_alloc_cipher("aes", 0, 0); if (IS_ERR(ctx->tfm)) { dbgprint(KERN_CRIT "Failed to alloc tfm for context %p\n", ctx); return PTR_ERR(ctx->tfm); } if (reset_prng_context(ctx, NULL, DEFAULT_PRNG_KSZ, NULL, NULL) < 0) return -EINVAL; /* * after allocation, we should always force the user to reset * so they don't inadvertently use the insecure default values * without specifying them intentially */ ctx->flags |= PRNG_NEED_RESET; return 0; } static void cprng_exit(struct crypto_tfm *tfm) { free_prng_context(crypto_tfm_ctx(tfm)); } static int cprng_get_random(struct crypto_rng *tfm, u8 *rdata, unsigned int dlen) { struct prng_context *prng = crypto_rng_ctx(tfm); return get_prng_bytes(rdata, dlen, prng); } /* * This is the cprng_registered reset method the seed value is * interpreted as the tuple { V KEY DT} * V and KEY are required during reset, and DT is optional, detected * as being present by testing the length of the seed */ static int cprng_reset(struct crypto_rng *tfm, u8 *seed, unsigned int slen) { struct prng_context *prng = crypto_rng_ctx(tfm); u8 *key = seed + DEFAULT_BLK_SZ; u8 *dt = NULL; if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ) return -EINVAL; if (slen >= (2 * DEFAULT_BLK_SZ + DEFAULT_PRNG_KSZ)) dt = key + DEFAULT_PRNG_KSZ; reset_prng_context(prng, key, DEFAULT_PRNG_KSZ, seed, dt); if (prng->flags & PRNG_NEED_RESET) return -EINVAL; return 0; } static struct crypto_alg rng_alg = { .cra_name = "stdrng", .cra_driver_name = "ansi_cprng", .cra_priority = 100, .cra_flags = CRYPTO_ALG_TYPE_RNG, .cra_ctxsize = sizeof(struct prng_context), .cra_type = &crypto_rng_type, .cra_module = THIS_MODULE, .cra_list = LIST_HEAD_INIT(rng_alg.cra_list), .cra_init = cprng_init, .cra_exit = cprng_exit, .cra_u = { .rng = { .rng_make_random = cprng_get_random, .rng_reset = cprng_reset, .seedsize = DEFAULT_PRNG_KSZ + 2*DEFAULT_BLK_SZ, } } }; /* Module initalization */ static int __init prng_mod_init(void) { if (fips_enabled) rng_alg.cra_priority += 200; return crypto_register_alg(&rng_alg); } static void __exit prng_mod_fini(void) { crypto_unregister_alg(&rng_alg); return; } MODULE_LICENSE("GPL"); MODULE_DESCRIPTION("Software Pseudo Random Number Generator"); MODULE_AUTHOR("Neil Horman <nhorman@tuxdriver.com>"); module_param(dbg, int, 0); MODULE_PARM_DESC(dbg, "Boolean to enable debugging (0/1 == off/on)"); module_init(prng_mod_init); module_exit(prng_mod_fini); MODULE_ALIAS("stdrng");