Began write-up on pass-check.sh

content/post/password_checker.md

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+---
+title: "Password Checking Script"
+date: 2019-04-13
+lastmod: 2019-04-13
+draft: true
+tags: ["linux","code"]
+categories: ["Blog"]
+contentCopyright: false
+hideHeaderAndFooter: false
+---
+Having been inspired by the HIBP[^1] password checker, I set out to write a
+script with the following goals:
+
+1. Check for duplicate/re-used passwords
+1. Check the strength of each password
+1. Check passwords against the `pwnedpass` API
+
+<!--more-->
+# Preface
+It's worth nothing that I use [`passwordstore`](https://www.passwordstore.org/)
+to generate, and manage my passwords. On mobile, this is done using the official
+[OpenKeychain](https://www.openkeychain.org/), and
+[Password Store](https://github.com/zeapo/Android-Password-Store). Passwords are
+shared across my devices using Git[^2]
+
+# Pump Your Brakes
+Instead of jumping right into checking all my passwords, in plain-text, against
+the `pwnedpasswords` API, it would be best to figure out how to safely transform
+them to `sha1sum`[^3]. The API supports sending the first 5 characters of a `sha1sum`,
+returning a list of all `sha1sum`s of exposed passwords (_with the exposed
+count_) for the user to verify them on their end.
+
+# Gathering Passwords
+The easiest way to get a comprehensive list (_associative array_[^4]) of
+passwords and their `pass` path was to use `find` to look for `*.gpg` files in
+my `.password-store` directory:
+```bash
+# Fetches all passwords in $PASSDIR and checks for duplicates (base check)
+getpws()
+{
+    # Loop over the find (newline-in-filename safe)
+    while read -r -d '' p; do
+        # Remove the root directory, and file extension
+        p=$(printf "%s" "$p" | sed "s|^$PASSDIR/||" | sed "s/.gpg//")
+
+        # Collect the trimmed, sha1 passwords
+        pwsha=$(pass "$p" | awk 'FNR==1 {printf "%s", $0}' | sha1sum | awk '{printf "%s", toupper($1)}')
+        pws["$p"]="$pwsha"
+    done < <(find "$PASSDIR" -name "*.gpg" -type f -print0)
+}
+```
+To note, `find` with `-print0` is used to avoid printing newline characters
+(_unlikely, but good practice_), so that we can utilize the null terminator `''`
+within `read -d ''`. Also, `read -r` simply prevents backslashes from being
+treated in a special way (_also good practice!_)[^5]
+
+It may be worth mentioning, to folks less familiar with `awk`, that the
+`FNR==1`, in this context, simply helps to get rid of any newline oddities from
+being piped into `sha1sum`. I discovered incorrect `sha1sum` values **without**
+`FNR==1` resulting in a useless password check!
+
+{{% admonition note Note %}}
+`IFS=` would not have fixed the above newline issue, as the problem stems
+from the output of `pass "$p"` and **not** the filenames.
+{{% /admonition %}}
+
+That takes care of gathering our passwords, but we'll revisit this again in the
+next part.
+
+# Sharing is not Caring
+The most efficient way of checking for duplicates was simply to iterate over the
+array of passwords gathered, and check against the current one found in the
+`getpws()` function's loop. The names of the duplicate passwords are stored in
+_another_ associative array for printing later as part of the "report".
+```bash
+# Checks for duplicate sha1sums of passwords in the associative array
+checkdupes()
+{
+    for i in "${!pws[@]}"; do
+        if [[ "$2" == "${pws[$i]}" ]]; then
+            pwdupes["$1"]="$i"
+        fi
+    done
+}
+```
+
+That being done, we just incorporate it into the above `getpws()` loop!
+```bash
+getpws()
+{
+    while read -r -d '' p; do
+        ...
+        checkdupes "$p" "$pwsha"
+    done < <(find "$PASSDIR" -name "*.gpg" -type f -print0)
+}
+```
+
+This accomplishes our *first goal* of checking duplicate passwords --
+**hooray!**
+
+Next up: _Passwortstärke_
+
+# TODO
+
+[^1]: [Have I Been Pwned](https://haveibeenpwned.com/Passwords)
+[^2]: [`pass` Extended Git Example](https://git.zx2c4.com/password-store/about/#EXTENDED%20GIT%20EXAMPLE)
+[^3]: [SHA-1 (Secure Hashing Algorithm)](https://en.wikipedia.org/wiki/SHA-1)
+[^4]: [Arrays (Bash Reference Manual)](https://www.gnu.org/software/bash/manual/html_node/Arrays.html)
+[^5]: [`man read`](https://linux.die.net/man/2/read)