From e328d6e77822d1c480f6da4d9c4c5247b307ecf3 Mon Sep 17 00:00:00 2001
From: Sonia Keys <soniakeys@gmail.com>
Date: Wed, 25 Jun 2014 00:12:17 -0400
Subject: [PATCH] new exercise diffie-hellman

---
 diffie-hellman.md  | 29 +++++++++++++++++++++++++++++
 diffie-hellman.yml |  4 ++++
 2 files changed, 33 insertions(+)
 create mode 100644 diffie-hellman.md
 create mode 100644 diffie-hellman.yml

diff --git a/diffie-hellman.md b/diffie-hellman.md
new file mode 100644
index 0000000000..98d6f1b396
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+++ b/diffie-hellman.md
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+Alice and Bob use Diffie-Hellman key exchange to share secrets.  They start with prime numbers, pick private keys, generate and share public keys, and then generate a shared secret key.
+
+## Step 0
+
+The test program supplies prime numbers p and g.
+
+## Step 1
+
+Alice picks a private key, a, greater than 1 and less than p.  Bob does the same to pick a private key b.
+
+## Step 2
+
+Alice calcuates a public key A.
+
+    A = g**a mod p
+
+Using the same p and g, Bob similarly calculates a public key B from his private key b.
+
+## Step 3
+
+Alice and Bob exchange public keys.  Alice calculates secret key s.
+
+    s = B**a mod p
+
+Bob calculates
+
+    s = A**b mod p
+
+The calculations produce the same result!  Alice and Bob now share secret s.
diff --git a/diffie-hellman.yml b/diffie-hellman.yml
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index 0000000000..43cebd86c3
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+++ b/diffie-hellman.yml
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+---
+blurb: "Diffie-Hellman key exchange."
+source: "Wikipedia, 1024 bit key from www.cryptopp.com/wiki."
+source_url: "http://en.wikipedia.org/wiki/Diffie%E2%80%93Hellman_key_exchange"