diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..bdc789e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/target
+todos.txt
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..7448778
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,64 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "bip39"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b9e89470017230c38e52b82b3ee3f530db1856ba1d434e3a67a3456a8a8dec5f"
+dependencies = [
+ "bitcoin_hashes",
+ "rand_core",
+ "serde",
+ "unicode-normalization",
+]
+
+[[package]]
+name = "bitcoin_hashes"
+version = "0.9.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7ce18265ec2324ad075345d5814fbeed4f41f0a660055dc78840b74d19b874b1"
+
+[[package]]
+name = "maybe-uninit"
+version = "2.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60302e4db3a61da70c0cb7991976248362f30319e88850c487b9b95bbf059e00"
+
+[[package]]
+name = "rand_core"
+version = "0.4.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9c33a3c44ca05fa6f1807d8e6743f3824e8509beca625669633be0acbdf509dc"
+
+[[package]]
+name = "seed-xor"
+version = "0.1.0"
+dependencies = [
+ "bip39",
+]
+
+[[package]]
+name = "serde"
+version = "1.0.128"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1056a0db1978e9dbf0f6e4fca677f6f9143dc1c19de346f22cac23e422196834"
+
+[[package]]
+name = "smallvec"
+version = "0.6.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b97fcaeba89edba30f044a10c6a3cc39df9c3f17d7cd829dd1446cab35f890e0"
+dependencies = [
+ "maybe-uninit",
+]
+
+[[package]]
+name = "unicode-normalization"
+version = "0.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09c8070a9942f5e7cfccd93f490fdebd230ee3c3c9f107cb25bad5351ef671cf"
+dependencies = [
+ "smallvec",
+]
diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..dbaf3f4
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,17 @@
+[package]
+name = "seed-xor"
+version = "0.1.0"
+edition = "2018"
+authors = ["KaiWitt <kaiwitt@protonmail.com>"]
+description = "XOR bip39 mnemonics."
+readme = "README.md"
+repository = "https://github.com/KaiWitt/seed-xor"
+license = "MIT"
+keywords = ["bitcoin", "seed", "mnemonic", "bip39", "xor"]
+categories = ["cryptography::cryptocurrencies"]
+publish = true
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+bip39 = "1.0.1"
\ No newline at end of file
diff --git a/README.md b/README.md
index e2c00b0..690e701 100644
--- a/README.md
+++ b/README.md
@@ -1 +1,35 @@
-# seed-xor
\ No newline at end of file
+# seed-xor
+
+seed-xor builds on top of [rust-bip39](https://github.com/rust-bitcoin/rust-bip39/)
+and lets you XOR bip39 mnemonics as defined in [Coldcards docs](https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md).
+
+
+It is also possible to XOR mnemonics with differing numbers of words.
+For this the shorter one will be extended with 0s during the XOR calculation.
+
+
+## Example
+
+```rust
+use seed_xor::Mnemonic;
+use std::str::FromStr;
+
+// Coldcard example: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+let a_str = "romance wink lottery autumn shop bring dawn tongue range crater truth ability miss spice fitness easy legal release recall obey exchange recycle dragon room";
+let b_str = "lion misery divide hurry latin fluid camp advance illegal lab pyramid unaware eager fringe sick camera series noodle toy crowd jeans select depth lounge";
+let c_str = "vault nominee cradle silk own frown throw leg cactus recall talent worry gadget surface shy planet purpose coffee drip few seven term squeeze educate";
+let result_str = "silent toe meat possible chair blossom wait occur this worth option bag nurse find fish scene bench asthma bike wage world quit primary indoor";
+
+// Mnemonic is a wrapper for bip39::Mnemonic which implements the XOR operation `^`.
+// Mnemonics can also be created from entropy.
+let a = Mnemonic::from_str(a_str).unwrap();
+let b = Mnemonic::from_str(b_str).unwrap();
+let c = Mnemonic::from_str(c_str).unwrap();
+let result = Mnemonic::from_str(result_str).unwrap();
+
+assert_eq!(result, a ^ b ^ c);
+```
+
+ ## Useful resources
+ - Coldcard docs: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+ - Easy bip39 mnemonic explanation: https://learnmeabitcoin.com/technical/mnemonic
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..7f9deba
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,185 @@
+//! # seed-xor
+//!
+//! seed-xor builds on top of [rust-bip39](https://github.com/rust-bitcoin/rust-bip39/)
+//! and lets you XOR bip39 mnemonics as defined in [Coldcards docs](https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md).
+//!
+//!
+//! It is also possible to XOR mnemonics with differing numbers of words.
+//! For this the shorter one will be extended with 0s during the XOR calculation.
+//!
+//!
+//! ## Example
+//!
+//! ```rust
+//! use seed_xor::Mnemonic;
+//! use std::str::FromStr;
+//!
+//! // Coldcard example: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+//! let a_str = "romance wink lottery autumn shop bring dawn tongue range crater truth ability miss spice fitness easy legal release recall obey exchange recycle dragon room";
+//! let b_str = "lion misery divide hurry latin fluid camp advance illegal lab pyramid unaware eager fringe sick camera series noodle toy crowd jeans select depth lounge";
+//! let c_str = "vault nominee cradle silk own frown throw leg cactus recall talent worry gadget surface shy planet purpose coffee drip few seven term squeeze educate";
+//! let result_str = "silent toe meat possible chair blossom wait occur this worth option bag nurse find fish scene bench asthma bike wage world quit primary indoor";
+//!
+//! // Mnemonic is a wrapper for bip39::Mnemonic which implements the XOR operation `^`.
+//! // Mnemonics can also be created from entropy.
+//! let a = Mnemonic::from_str(a_str).unwrap();
+//! let b = Mnemonic::from_str(b_str).unwrap();
+//! let c = Mnemonic::from_str(c_str).unwrap();
+//! let result = Mnemonic::from_str(result_str).unwrap();
+//!
+//! assert_eq!(result, a ^ b ^ c);
+//! ```
+//!
+use std::{
+    fmt,
+    ops::{BitXor, BitXorAssign},
+    str::FromStr,
+};
+
+use bip39::Mnemonic as Inner;
+
+/// Wrapper for a [bip39::Mnemonic] which is aliased as `Inner`.
+#[derive(Clone, PartialEq, Eq, Debug, Hash, PartialOrd, Ord)]
+pub struct Mnemonic {
+    /// Actual [bip39::Mnemonic] which is wrapped to be able to implement the XOR operator.
+    inner: Inner,
+}
+
+impl Mnemonic {
+    /// Private constructor.
+    fn new(inner: Inner) -> Self {
+        Mnemonic { inner }
+    }
+
+    /// Access the private inner [bip39::Mnemonic] for more functionality.
+    pub fn inner(&self) -> &Inner {
+        &self.inner
+    }
+
+    /// Wrapper for the same method as in [bip39::Mnemonic].
+    pub fn from_entropy(entropy: &[u8]) -> Result<Self, bip39::Error> {
+        match Inner::from_entropy(entropy) {
+            Ok(inner) => Ok(Mnemonic::new(inner)),
+            Err(err) => Err(err),
+        }
+    }
+
+    /// XOR two [Mnemonic]s without consuming them.
+    /// If consumption is not of relevance the XOR operator `^` and XOR assigner `^=` can be used as well.
+    fn xor(&self, rhs: &Self) -> Self {
+        let mut entropy = self.inner.to_entropy();
+        let xor_values = rhs.inner.to_entropy();
+
+        // XOR each Byte
+        entropy
+            .iter_mut()
+            .zip(xor_values.iter())
+            .for_each(|(a, b)| *a ^= b);
+
+        // Extend entropy with values of xor_values if it has a shorter entropy length.
+        if entropy.len() < xor_values.len() {
+            entropy.extend(xor_values.iter().skip(entropy.len()))
+        }
+
+        // We unwrap here because entropy has either as many Bytes
+        // as self or rhs and both are valid mnemonics.
+        Mnemonic::from_entropy(&entropy).unwrap()
+    }
+}
+
+impl FromStr for Mnemonic {
+    type Err = bip39::Error;
+
+    fn from_str(mnemonic: &str) -> Result<Self, <Self as FromStr>::Err> {
+        match Inner::from_str(mnemonic) {
+            Ok(inner) => Ok(Mnemonic::new(inner)),
+            Err(err) => Err(err),
+        }
+    }
+}
+
+impl fmt::Display for Mnemonic {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        for (i, word) in self.inner.word_iter().enumerate() {
+            if i > 0 {
+                f.write_str(" ")?;
+            }
+            f.write_str(word)?;
+        }
+        Ok(())
+    }
+}
+
+impl BitXor for Mnemonic {
+    type Output = Self;
+
+    fn bitxor(self, rhs: Self) -> Self::Output {
+        self.xor(&rhs)
+    }
+}
+
+impl BitXorAssign for Mnemonic {
+    fn bitxor_assign(&mut self, rhs: Self) {
+        *self = self.xor(&rhs)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::Mnemonic;
+    use std::str::FromStr;
+
+    #[test]
+    fn seed_xor_works() {
+        // Coldcard example: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+        let a_str = "romance wink lottery autumn shop bring dawn tongue range crater truth ability miss spice fitness easy legal release recall obey exchange recycle dragon room";
+        let b_str = "lion misery divide hurry latin fluid camp advance illegal lab pyramid unaware eager fringe sick camera series noodle toy crowd jeans select depth lounge";
+        let c_str = "vault nominee cradle silk own frown throw leg cactus recall talent worry gadget surface shy planet purpose coffee drip few seven term squeeze educate";
+        let result_str = "silent toe meat possible chair blossom wait occur this worth option bag nurse find fish scene bench asthma bike wage world quit primary indoor";
+
+        let a = Mnemonic::from_str(a_str).unwrap();
+        let b = Mnemonic::from_str(b_str).unwrap();
+        let c = Mnemonic::from_str(c_str).unwrap();
+        let result = Mnemonic::from_str(result_str).unwrap();
+
+        assert_eq!(result, a.clone() ^ b.clone() ^ c.clone());
+        assert_eq!(result, b ^ c ^ a); // Commutative
+    }
+
+    #[test]
+    fn seed_xor_assignment_works() {
+        // Coldcard example: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+        let a_str = "romance wink lottery autumn shop bring dawn tongue range crater truth ability miss spice fitness easy legal release recall obey exchange recycle dragon room";
+        let b_str = "lion misery divide hurry latin fluid camp advance illegal lab pyramid unaware eager fringe sick camera series noodle toy crowd jeans select depth lounge";
+        let c_str = "vault nominee cradle silk own frown throw leg cactus recall talent worry gadget surface shy planet purpose coffee drip few seven term squeeze educate";
+        let result_str = "silent toe meat possible chair blossom wait occur this worth option bag nurse find fish scene bench asthma bike wage world quit primary indoor";
+
+        let a = Mnemonic::from_str(a_str).unwrap();
+        let b = Mnemonic::from_str(b_str).unwrap();
+        let c = Mnemonic::from_str(c_str).unwrap();
+        let result = Mnemonic::from_str(result_str).unwrap();
+
+        let mut assigned = a.xor(&b); // XOR without consuming
+        assigned ^= c;
+
+        assert_eq!(result, assigned);
+    }
+
+    #[test]
+    fn seed_xor_with_different_lengths_works() {
+        // Coldcard example: https://github.com/Coldcard/firmware/blob/master/docs/seed-xor.md
+        // but truncated mnemonics with correct last word.
+        let str_24 = "romance wink lottery autumn shop bring dawn tongue range crater truth ability miss spice fitness easy legal release recall obey exchange recycle dragon room";
+        let str_16 = "lion misery divide hurry latin fluid camp advance illegal lab pyramid unaware eager fringe sick camera series number";
+        let str_12 = "vault nominee cradle silk own frown throw leg cactus recall talent wisdom";
+        let result_str = "silent toe meat possible chair blossom wait occur this worth option aware since milk mother grace rocket cement recall obey exchange recycle dragon rocket";
+
+        let w_24 = Mnemonic::from_str(str_24).unwrap();
+        let w_16 = Mnemonic::from_str(str_16).unwrap();
+        let w_12 = Mnemonic::from_str(str_12).unwrap();
+        let result = Mnemonic::from_str(result_str).unwrap();
+
+        assert_eq!(result, w_24.clone() ^ w_16.clone() ^ w_12.clone());
+        assert_eq!(result, w_12 ^ w_24 ^ w_16); // Commutative
+    }
+}