1 files changed, 74 insertions, 0 deletions
diff --git a/src/home/modhex.c b/src/home/modhex.c
new file mode 100644
index 0000000..ae5f895
--- /dev/null
+++ b/src/home/modhex.c
@@ -0,0 +1,74 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <errno.h>
+
+#include "modhex.h"
+#include "macro.h"
+#include "memory-util.h"
+
+const char modhex_alphabet[16] = {
+        'c', 'b', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'n', 'r', 't', 'u', 'v'
+};
+
+int decode_modhex_char(char x) {
+
+        for (size_t i = 0; i < ELEMENTSOF(modhex_alphabet); i++)
+                /* Check both upper and lowercase */
+                if (modhex_alphabet[i] == x || (modhex_alphabet[i] - 32) == x)
+                        return i;
+
+        return -EINVAL;
+}
+
+int normalize_recovery_key(const char *password, char **ret) {
+        _cleanup_(erase_and_freep) char *mangled = NULL;
+        size_t l;
+
+        assert(password);
+        assert(ret);
+
+        l = strlen(password);
+        if (!IN_SET(l,
+                    MODHEX_RAW_LENGTH*2,          /* syntax without dashes */
+                    MODHEX_FORMATTED_LENGTH-1))   /* syntax with dashes */
+                return -EINVAL;
+
+        mangled = new(char, MODHEX_FORMATTED_LENGTH);
+        if (!mangled)
+                return -ENOMEM;
+
+        for (size_t i = 0, j = 0; i < MODHEX_RAW_LENGTH; i++) {
+                size_t k;
+                int a, b;
+
+                if (l == MODHEX_RAW_LENGTH*2)
+                        /* Syntax without dashes */
+                        k = i * 2;
+                else {
+                        /* Syntax with dashes */
+                        assert(l == MODHEX_FORMATTED_LENGTH-1);
+                        k = i * 2 + i / 4;
+
+                        if (i > 0 && i % 4 == 0 && password[k-1] != '-')
+                                return -EINVAL;
+                }
+
+                a = decode_modhex_char(password[k]);
+                if (a < 0)
+                        return -EINVAL;
+                b = decode_modhex_char(password[k+1]);
+                if (b < 0)
+                        return -EINVAL;
+
+                mangled[j++] = modhex_alphabet[a];
+                mangled[j++] = modhex_alphabet[b];
+
+                if (i % 4 == 3)
+                        mangled[j++] = '-';
+        }
+
+        mangled[MODHEX_FORMATTED_LENGTH-1] = 0;
+
+        *ret = TAKE_PTR(mangled);
+        return 0;
+}