From cd7b218e51783fd75292e04a81672079d665c0dc Mon Sep 17 00:00:00 2001
From: Andrew Dirksen <andrew@dirksen.com>
Date: Mon, 13 May 2019 10:10:19 -0700
Subject: [PATCH] Copy docs to readme, link to repo from Cargo.toml.
 https://www.reddit.com/r/rust/comments/bn48nz/pow_sha256_based_proofs_of_work_over_typed_data/en2bcxx?utm_source=share&utm_medium=web2x

---
 Cargo.toml |  6 ++--
 readme.md  | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
 src/lib.rs |  2 +-
 3 files changed, 88 insertions(+), 5 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index d242434..90e7eb7 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,15 +1,17 @@
 [package]
 name = "pow"
-version = "0.1.2"
+version = "0.1.3"
 authors = ["Andrew Dirksen <andrew@dirksen.com>"]
 description = """
 Generate or verify sha256 based proofs of work over arbitrary typed data.
 """
 edition = "2018"
 documentation = "https://docs.rs/pow"
-tags = ["proof of work", "pw set", "powtag", "tag"]
+keywords = ["pwset", "powtag", "tag"]
 readme = "readme.md"
 license = "MIT OR Apache-2.0"
+repository = "https://github.com/bddap/pow"
+categories = [] # pr me!
 
 [dependencies]
 sha2 = "0.8.0"
diff --git a/readme.md b/readme.md
index 3657cfc..84ae47b 100644
--- a/readme.md
+++ b/readme.md
@@ -1,5 +1,86 @@
 # Pow
 
-Typed proof of work tags.
+Sha256 based proof of work over a typed piece of data.
 
-[docs](https://docs.rs/pow)
+Any type that implementes serde::Deserialize can be tagged with a proof of work.
+
+# Examples
+
+Prove we did work targeting a phrase.
+
+```
+use pow::Pow;
+
+// very easy mode
+let difficulty = u128::max_value() - u128::max_value() / 2;
+
+let phrase = b"Phrase to tag.".to_vec();
+let pw = Pow::prove_work(&phrase, difficulty).unwrap();
+assert!(pw.score(&phrase).unwrap() >= difficulty);
+```
+
+Prove more difficult work. This time targeting a time.
+
+```
+// more diffcult, takes around 100_000 hashes to generate proof
+let difficulty = u128::max_value() - u128::max_value() / 100_000;
+
+let now: u64 = get_unix_time_seconds();
+let pw = Pow::prove_work(&now, difficulty).unwrap();
+assert!(pw.score(&now).unwrap() >= difficulty);
+```
+
+# Score scheme
+
+To score a proof of work for a given (target, Pow) pair:
+Sha256 is calculated over the concatenation SALT + target + Pow.
+The first 16 bytes of the hash are interpreted as a 128 bit unsigned integer.
+That integer is the score.
+A constant, SALT, is used as prefix to prevent pow reuse from other systems such as proof
+of work blockchains.
+
+In other words:
+
+```
+fn score<T: Serialize>(target: &T, pow_tag: &Pow<T>) -> u128 {
+    let bytes = serialize(&SALT) + serialize(target) + serialize(pow_tag);
+    let hash = sha256(&bytes);
+    deserialize(&hash[..16])
+}
+```
+
+# Serialization encoding.
+
+It shouldn't matter to users of this library, but the bincode crate is used for cheap
+deterministic serialization. All values are serialized using network byte order.
+
+# Threshold scheme
+
+Given a minimum score m. A Pow p satisfies the minimum score for target t iff score(t, p) >= m.
+
+# Choosing a difficulty setting.
+
+Difficulty settings are usually best adjusted dynamically a la bitcoin.
+
+To manually select a difficulty, choose the average number of hashes required.
+
+```
+fn difficulty(average: u128) -> u128 {
+    debug_assert_ne!(average, 0, "It is impossible to prove work in zero attempts.");
+    let m = u128::max_value();
+    m - m / average
+}
+```
+
+Conversely, to calculate probable number of hashes required to satisfy a given minimum
+difficulty.
+
+```
+fn average(difficulty: u128) -> u128 {
+    let m = u128::max_value();
+    if difficulty == m {
+        return m;
+    } 
+    m / (m - difficulty)
+}
+```
diff --git a/src/lib.rs b/src/lib.rs
index b697e56..5896291 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -63,7 +63,7 @@
 //! # Serialization encoding.
 //!
 //! It shouldn't matter to users of this library, but the bincode crate is used for cheap
-//! derterministic serialization. All values are serialized using network byte order.
+//! deterministic serialization. All values are serialized using network byte order.
 //!
 //! # Threshold scheme
 //!