cryptopals

commit 4b307a8b848020c4b29634f00ff97ccc8be2ab1f
parent af9473f3e1f4649c88cae9ba4fc775fef84044ec
Author: Jared Tobin <jared@jtobin.ca>
Date:   Sat, 26 Aug 2017 19:20:37 +1200

Misc updates.

Diffstat:
M
README.md
 | 
3
++-
M
docs/s2.md
 | 
44
+++++++++++++++++++++++++++++++++++++++++++-
M
lib/ecb_detector/src/main.rs
 | 
4
++--

3 files changed, 47 insertions(+), 4 deletions(-)
diff --git a/README.md b/README.md
@@ -3,7 +3,8 @@
 [![MIT License](https://img.shields.io/badge/license-MIT-blue.svg)](https://github.com/jtobin/cryptopals/blob/master/LICENSE)
 
 Matasano's [cryptopals challenges](http://cryptopals.com/), implemented mainly
-in [Rust](https://www.rust-lang.org) and [Haskell](https://haskell-lang.org/).
+in [Rust](https://www.rust-lang.org) and [Haskell](https://haskell-lang.org/)
+(with plenty of help from bash and friends).
 
 ## Problems
 
diff --git a/docs/s2.md b/docs/s2.md
@@ -2,6 +2,10 @@
 
 #### 2.9
 
+PKCS #7 padding here just means that to pad a message of length 'l' to 'k'
+bytes, one appends 'k - l' bytes -- each of value 'k - l' -- to the message.
+So here we get four bytes' worth of padding, each of value 04:
+
     $ echo -n 'YELLOW SUBMARINE' | ./bin/pkcs 20 | xxd
     00000000: 5945 4c4c 4f57 2053 5542 4d41 5249 4e45  YELLOW SUBMARINE
     00000010: 0404 0404 0a                             .....
@@ -17,10 +21,48 @@ Using OpenSSL:
     I'm back and I'm ringin' the bell
     A rockin' on the mike while the fly girls yell
 
-Here's an answer that I had to write code to get:
+Or, here's an answer that I had to write code to get:
 
     $ cat data/s2/q10_input.txt | tr -d '\n' | \
         ./bin/aes_cbc --key "YELLOW SUBMARINE" | head -2
     I'm back and I'm ringin' the bell
     A rockin' on the mike while the fly girls yell
 
+#### 2.11
+
+I'm having fun with the shell so I was originally going to string this all
+together with bash.  One could generate keys/IVs like so (note the use of
+LC_CTYPE in order to get 'tr' to work properly on OS X):
+
+    $ AES_KEY=$(LC_CTYPE=C tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c16)
+    $ IV=$(LC_CTYPE=C tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c16)
+
+and flip a coin:
+
+    $ HEAD=$(($RANDOM % 2))
+
+and even come up with some random bytes to prepend and append:
+
+    $ NPREPEND=$(jot -r 1 5 10) NAPPEND=$(jot -r 1 5 10)
+    $ PREPENDER=$(LC_CTYPE=C tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c$NPREPEND)
+    $ APPENDER=$(LC_CTYPE=C tr -dc 'a-zA-Z0-9' < /dev/urandom | head -c$NAPPEND)
+    $ echo 'message' | sed -e "s/^/$PREPENDER/;s/$/$APPENDER/"
+    ifqfc9FshtmessagekOIxmrYfR
+
+So you could do something crazy, like:
+
+    $ echo 'message' | sed -e "s/^/$PREPENDER/;s/$/$APPENDER/" | \
+        base64 | tr -d '\n' | if [[ $HEAD == 0]]; \
+          then ./bin/aes_ecb --encrypt -k $AES_KEY; \
+          else ./bin/aes_cbc --encrypt -k $AES_KEY --iv $IV; fi
+    zcE4rONdRk04w8v4Sm8HYQ==
+
+and then:
+
+    $ echo "zcE4rONdRk04w8v4Sm8HYQ==" | ./bin/ecb_detector
+    likely cbc
+
+which is actually the wrong guess here.
+
+But, uh, let's not use bash for this.
+
diff --git a/lib/ecb_detector/src/main.rs b/lib/ecb_detector/src/main.rs
@@ -6,10 +6,10 @@ use std::io::{self, Read};
 
 const KEY_SIZE: usize = 16;
 
-fn ecb_detector(encoded: &[u8], size: usize) -> bool {
+fn ecb_detector(ciphertext: &[u8], size: usize) -> bool {
     let mut blocks = HashSet::new();
 
-    for block in encoded.chunks(size) {
+    for block in ciphertext.chunks(size) {
         if blocks.contains(block) {
             return true;
         }