From d314d0cf4b92e1dd9c1f761498b06160dcf5e104 Mon Sep 17 00:00:00 2001
From: Samuel Fadel <samuel@nihil.ws>
Date: Sat, 8 Apr 2023 20:12:35 +0200
Subject: Initial commit.

An initial working implementation of the password generating algorithm
of lesspass. Lacks any sort of documentation or usage info and simply
prints the generated password on stdout.

* lpass.c: Initial implementation of lesspass
* Makefile: A just works version
---
 lpass.c | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 163 insertions(+)
 create mode 100644 lpass.c

(limited to 'lpass.c')

diff --git a/lpass.c b/lpass.c
new file mode 100644
index 0000000..2193359
--- /dev/null
+++ b/lpass.c
@@ -0,0 +1,163 @@
+#include <openssl/bn.h>
+#include <openssl/evp.h>
+
+#include <stdint.h>
+#include <stdio.h>
+#include <string.h>
+
+#define MAX_BUF 1024
+#define ENTROPY_ITERATIONS 100000
+#define ENTROPY_KEY_LENGTH 32
+
+#define CHAR_SUBSET_LOWER "abcdefghijklmnopqrstuvwxyz"
+#define CHAR_SUBSET_UPPER "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+#define CHAR_SUBSET_DIGITS "0123456789"
+#define CHAR_SUBSET_SYMBOLS "!\"#$%&'()*+,-./:;<=>?@[\\]^_`{|}~"
+
+const char *CHAR_SET = (CHAR_SUBSET_LOWER
+                        CHAR_SUBSET_UPPER
+                        CHAR_SUBSET_DIGITS
+                        CHAR_SUBSET_SYMBOLS);
+
+static BIGNUM *
+calc_entropy(const char *site,
+             const char *login,
+             uint64_t counter,
+             const char *master_pass,
+             int passlen)
+{
+    char salt[MAX_BUF + 1];
+    memset(salt, 0, sizeof(salt));
+    int saltlen = snprintf(salt, MAX_BUF, "%s%s%lx", site, login, counter);
+    if (saltlen > MAX_BUF) {
+        return 0;
+    }
+
+    unsigned char key[ENTROPY_KEY_LENGTH];
+    memset(key, 0, sizeof(key));
+    int status = PKCS5_PBKDF2_HMAC(master_pass, passlen,
+                                   (const unsigned char *) salt, saltlen,
+                                   ENTROPY_ITERATIONS,
+                                   EVP_sha256(),
+                                   ENTROPY_KEY_LENGTH,
+                                   key);
+    if (status == 0) {
+        return 0;
+    }
+
+    /* NULL as last arg to allocate a new BIGNUM */
+    return BN_bin2bn(key, ENTROPY_KEY_LENGTH, NULL);
+}
+
+static int
+consume_entropy(char *generated_pass, BIGNUM *entropy, const char *charset, int maxlen)
+{
+    int retval = 1;
+    BN_CTX *ctx = BN_CTX_new();
+    BIGNUM *bn_charsetlen = BN_new();
+    BIGNUM *bn_remainder = BN_new();
+    int charsetlen = strlen(charset);
+    BN_set_word(bn_charsetlen, charsetlen);
+    for (int passlen = strlen(generated_pass);
+         passlen < maxlen;
+         passlen++) {
+        BN_div(entropy, bn_remainder, entropy, bn_charsetlen, ctx);
+        int remainder = BN_get_word(bn_remainder);
+        if (remainder >= charsetlen) {
+            retval = 0;
+            goto consume_entropy_cleanup;
+        }
+        generated_pass[passlen] = charset[remainder];
+    }
+consume_entropy_cleanup:
+    BN_free(bn_remainder);
+    BN_free(bn_charsetlen);
+    BN_CTX_free(ctx);
+    return retval;
+}
+
+static int
+insert_str_pseudo_randomly(char *generated_pass, BIGNUM *entropy, const char *s)
+{
+    int retval = 1;
+    char buf[MAX_BUF + 1];
+    uint64_t passlen = (uint64_t) strlen(generated_pass);
+    BN_CTX *ctx = BN_CTX_new();
+    BIGNUM *bn_passlen = BN_new();
+    BIGNUM *bn_remainder = BN_new();
+    for (char c = *s; *s != '\0'; c = *(++s)) {
+        if (BN_set_word(bn_passlen, passlen) == 0) {
+            retval = 0;
+            goto insert_str_pseudo_randomly_cleanup;
+        }
+        BN_div(entropy, bn_remainder, entropy, bn_passlen, ctx);
+        uint64_t remainder = BN_get_word(bn_remainder);
+        /*
+         * Idea here is to add the char `c` at position `remainder` in `generated_pass`.
+         * 1. Copy the part that would need to be shifted into `buf`.
+         */
+        memset(buf, 0, sizeof(buf));
+        strncpy(buf, &generated_pass[remainder], passlen - remainder);
+        /*
+         * 2. Add new character, then copy `buf` back into `generated_pass`.
+         */
+        generated_pass[remainder] = c;
+        strncpy(&generated_pass[remainder + 1], buf, passlen - remainder);
+        passlen++;
+    }
+insert_str_pseudo_randomly_cleanup:
+    BN_free(bn_remainder);
+    BN_free(bn_passlen);
+    BN_CTX_free(ctx);
+    return retval;
+}
+
+static void
+render_pass(BIGNUM *entropy, char *out, int length)
+{
+    /* XXX: FIXME: implement charset restrictions */
+    int num_charsets = 4;
+    consume_entropy(out, entropy, CHAR_SET, length - num_charsets);
+
+    /*
+     * After generating the initial password, add one character of
+     * each charset to ensure at least one is there.
+     */
+    char str_to_add[num_charsets + 1];
+    memset(str_to_add, 0, sizeof(str_to_add));
+    consume_entropy(&str_to_add[0], entropy, CHAR_SUBSET_LOWER, 1);
+    consume_entropy(&str_to_add[1], entropy, CHAR_SUBSET_UPPER, 1);
+    consume_entropy(&str_to_add[2], entropy, CHAR_SUBSET_DIGITS, 1);
+    consume_entropy(&str_to_add[3], entropy, CHAR_SUBSET_SYMBOLS, 1);
+    insert_str_pseudo_randomly(out, entropy, str_to_add);
+}
+
+int
+main(int argc, char *argv[])
+{
+    if (argc != 5) {
+        return 1;
+    }
+
+    const char *master_pass = argv[1];
+    int passlen = strlen(master_pass);
+    const char *site = argv[2];
+    const char *login = argv[3];
+    int length = 0;
+    if (sscanf(argv[4], "%d", &length) == 0) {
+        return 1;
+    }
+
+    uint64_t counter = 1;
+    BIGNUM *entropy = calc_entropy(site, login, counter, master_pass, passlen);
+    if (entropy == NULL) {
+        return 1;
+    }
+
+    char generated_pass[length + 1];
+    memset(generated_pass, 0, sizeof(generated_pass));
+    render_pass(entropy, generated_pass, length);
+    printf("%s\n", generated_pass);
+    BN_free(entropy);
+    return 0;
+}
-- 
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