1 files changed, 64 insertions, 0 deletions
diff --git a/packages/meshbay-cli/src/meshbay_cli/client/passphrase.py b/packages/meshbay-cli/src/meshbay_cli/client/passphrase.py
new file mode 100644
index 0000000..071c708
--- /dev/null
+++ b/packages/meshbay-cli/src/meshbay_cli/client/passphrase.py
@@ -0,0 +1,64 @@
+"""
+A new passphrase's floor, and the hub's proof of work — both checked here.
+
+The hub never sees a passphrase (docs/MESHBAY_DESIGN.md §3.1), so the floor —
+12 characters and about 60 estimated bits — can only be enforced by the client:
+`auth-page.js` `passwordBits`, the same estimate, so a passphrase the page
+refuses is refused here too.
+"""
+
+import hashlib
+import math
+import re
+
+MIN_LENGTH = 12
+MIN_BITS = 60
+_WEAK = re.compile(r"(password|motdepasse|azerty|qwerty|123456|meshbay)", re.I)
+
+
+def passphrase_bits(pw: str) -> int:
+    if not pw:
+        return 0
+    pool = 0
+    if re.search(r"[a-z]", pw):
+        pool += 26
+    if re.search(r"[A-Z]", pw):
+        pool += 26
+    if re.search(r"[0-9]", pw):
+        pool += 10
+    if re.search(r"[^A-Za-z0-9]", pw):
+        pool += 32
+    # JavaScript counts UTF-16 units; a character outside the BMP is two.
+    length = len(pw.encode("utf-16-le")) // 2
+    bits = length * math.log2(pool or 1)
+    if len(set(pw)) < length / 2:
+        bits *= 0.6
+    if re.fullmatch(r"[0-9]+", pw):
+        bits *= 0.5
+    if _WEAK.search(pw):
+        bits *= 0.3
+    # Math.round: halves go up.
+    return math.floor(bits + 0.5)
+
+
+def passphrase_problem(pw: str) -> str | None:
+    """Why a new passphrase is refused, or None."""
+    if len(pw.encode("utf-16-le")) // 2 < MIN_LENGTH:
+        return f"A passphrase has {MIN_LENGTH} characters at least."
+    if passphrase_bits(pw) < MIN_BITS:
+        return ("This passphrase is too easy to guess: make it longer, or mix in "
+                "other kinds of characters.")
+    return None
+
+
+def solve_captcha(challenge: dict) -> str | None:
+    """
+    The answer to `GET /v1/users/captcha`: the number below `max_number` whose
+    `<prefix><number>` hashes to `challenge` (`captcha.js` `solve`), as the token
+    the register and reset-request bodies carry. None if there is none.
+    """
+    prefix, want = challenge["prefix"], bytes.fromhex(challenge["challenge"])
+    for n in range(int(challenge["max_number"])):
+        if hashlib.sha256(f"{prefix}{n}".encode()).digest() == want:
+            return f"{prefix}{n}.{challenge['signature']}"
+    return None