/*
 * 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>

#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 succeeded, <0 if something went wrong
 */
static int _get_more_prng_bytes(struct prng_context *ctx, int cont_test)
{
        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 (cont_test) {
                                        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,
                                int do_cont_test)
{
        unsigned char *ptr = buf;
        unsigned int byte_count = (unsigned int)nbytes;
        int err;


        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;
        }

        /*
         * Return 0 in case of success as mandated by the kernel
         * crypto API interface definition.
         */
        err = 0;

        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, do_cont_test) < 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:
                while (ctx->rand_data_valid < DEFAULT_BLK_SZ) {
                        *ptr = ctx->rand_data[ctx->rand_data_valid];
                        ptr++;
                        byte_count--;
                        ctx->rand_data_valid++;
                        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, do_cont_test) < 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,
                              const unsigned char *key, size_t klen,
                              const unsigned char *V, const unsigned char *DT)
{
        int ret;
        const 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,
                            const u8 *src, unsigned int slen,
                            u8 *rdata, unsigned int dlen)
{
        struct prng_context *prng = crypto_rng_ctx(tfm);

        return get_prng_bytes(rdata, dlen, prng, 0);
}

/*
 *  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,
                       const u8 *seed, unsigned int slen)
{
        struct prng_context *prng = crypto_rng_ctx(tfm);
        const u8 *key = seed + DEFAULT_BLK_SZ;
        const 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;
}

#ifdef CONFIG_CRYPTO_FIPS
static int fips_cprng_get_random(struct crypto_rng *tfm,
                                 const u8 *src, unsigned int slen,
                                 u8 *rdata, unsigned int dlen)
{
        struct prng_context *prng = crypto_rng_ctx(tfm);

        return get_prng_bytes(rdata, dlen, prng, 1);
}

static int fips_cprng_reset(struct crypto_rng *tfm,
                            const u8 *seed, unsigned int slen)
{
        u8 rdata[DEFAULT_BLK_SZ];
        const u8 *key = seed + DEFAULT_BLK_SZ;
        int rc;

        struct prng_context *prng = crypto_rng_ctx(tfm);

        if (slen < DEFAULT_PRNG_KSZ + DEFAULT_BLK_SZ)
                return -EINVAL;

        /* fips strictly requires seed != key */
        if (!memcmp(seed, key, DEFAULT_PRNG_KSZ))
                return -EINVAL;

        rc = cprng_reset(tfm, seed, slen);

        if (!rc)
                goto out;

        /* this primes our continuity test */
        rc = get_prng_bytes(rdata, DEFAULT_BLK_SZ, prng, 0);
        prng->rand_data_valid = DEFAULT_BLK_SZ;

out:
        return rc;
}
#endif

static struct rng_alg rng_algs[] = { {
        .generate               = cprng_get_random,
        .seed                   = cprng_reset,
        .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
        .base                   =       {
                .cra_name               = "stdrng",
                .cra_driver_name        = "ansi_cprng",
                .cra_priority           = 100,
                .cra_ctxsize            = sizeof(struct prng_context),
                .cra_module             = THIS_MODULE,
                .cra_init               = cprng_init,
                .cra_exit               = cprng_exit,
        }
#ifdef CONFIG_CRYPTO_FIPS
}, {
        .generate               = fips_cprng_get_random,
        .seed                   = fips_cprng_reset,
        .seedsize               = DEFAULT_PRNG_KSZ + 2 * DEFAULT_BLK_SZ,
        .base                   =       {
                .cra_name               = "fips(ansi_cprng)",
                .cra_driver_name        = "fips_ansi_cprng",
                .cra_priority           = 300,
                .cra_ctxsize            = sizeof(struct prng_context),
                .cra_module             = THIS_MODULE,
                .cra_init               = cprng_init,
                .cra_exit               = cprng_exit,
        }
#endif
} };

/* Module initalization */
static int __init prng_mod_init(void)
{
        return crypto_register_rngs(rng_algs, ARRAY_SIZE(rng_algs));
}

static void __exit prng_mod_fini(void)
{
        crypto_unregister_rngs(rng_algs, ARRAY_SIZE(rng_algs));
}

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_CRYPTO("stdrng");
MODULE_ALIAS_CRYPTO("ansi_cprng");