diff --git a/Cargo.lock b/Cargo.lock
index 15921e9..7071c72 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,99 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "block-buffer"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3078c7629b62d3f0439517fa394996acacc5cbc91c5a20d8c658e77abd503a71"
+dependencies = [
+ "generic-array",
+]
+
+[[package]]
+name = "cfg-if"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "baf1de4339761588bc0619e3cbc0120ee582ebb74b53b4efbf79117bd2da40fd"
+
+[[package]]
+name = "cpufeatures"
+version = "0.2.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3e4c1eaa2012c47becbbad2ab175484c2a84d1185b566fb2cc5b8707343dfe58"
+dependencies = [
+ "libc",
+]
+
+[[package]]
+name = "crypto-common"
+version = "0.1.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1bfb12502f3fc46cca1bb51ac28df9d618d813cdc3d2f25b9fe775a34af26bb3"
+dependencies = [
+ "generic-array",
+ "typenum",
+]
+
+[[package]]
+name = "digest"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8168378f4e5023e7218c89c891c0fd8ecdb5e5e4f18cb78f38cf245dd021e76f"
+dependencies = [
+ "block-buffer",
+ "crypto-common",
+]
+
 [[package]]
 name = "gateway"
 version = "0.1.0"
+dependencies = [
+ "hex",
+ "sha2",
+]
+
+[[package]]
+name = "generic-array"
+version = "0.14.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85649ca51fd72272d7821adaf274ad91c288277713d9c18820d8499a7ff69e9a"
+dependencies = [
+ "typenum",
+ "version_check",
+]
+
+[[package]]
+name = "hex"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
+
+[[package]]
+name = "libc"
+version = "0.2.142"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a987beff54b60ffa6d51982e1aa1146bc42f19bd26be28b0586f252fccf5317"
+
+[[package]]
+name = "sha2"
+version = "0.10.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "82e6b795fe2e3b1e845bafcb27aa35405c4d47cdfc92af5fc8d3002f76cebdc0"
+dependencies = [
+ "cfg-if",
+ "cpufeatures",
+ "digest",
+]
+
+[[package]]
+name = "typenum"
+version = "1.16.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "497961ef93d974e23eb6f433eb5fe1b7930b659f06d12dec6fc44a8f554c0bba"
+
+[[package]]
+name = "version_check"
+version = "0.9.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "49874b5167b65d7193b8aba1567f5c7d93d001cafc34600cee003eda787e483f"
diff --git a/Cargo.toml b/Cargo.toml
index c033627..ba2b721 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -6,3 +6,5 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+sha2 = "0.10.6"
+hex = "0.4.3"
diff --git a/src/main.rs b/src/main.rs
index e7a11a9..cb8a4ca 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,3 +1,13 @@
+mod origin;
+
+use crate::origin::Descr;
+
 fn main() {
-    println!("Hello, world!");
+
+    let d = Descr::Git{
+        url: "foo",
+        branch: "bar",
+    };
+
+    println!("{}", d.id());
 }
diff --git a/src/origin.rs b/src/origin.rs
new file mode 100644
index 0000000..6fbd881
--- /dev/null
+++ b/src/origin.rs
@@ -0,0 +1,44 @@
+use sha2::{Sha256, Digest};
+use hex::ToHex;
+
+/// A unique description of an origin, from where a domain might be served.
+pub enum Descr<'a> {
+    Git{url: &'a str, branch: &'a str},
+}
+
+impl<'a> Descr<'a> {
+
+    /// Returns a globally unique string for the Descr.
+    pub fn id(&'a self) -> String {
+
+        let mut h = Sha256::new();
+
+        let mut h_update = |b: &str| {
+            h.update(b);
+            h.update("\n");
+        };
+
+        match self {
+            Descr::Git{url, branch} => {
+                h_update("git");
+                h_update(url);
+                h_update(branch);
+            }
+        }
+
+        h.finalize().encode_hex::<String>()
+    }
+}
+
+#[cfg(test)]
+mod descr_tests {
+
+    #[test]
+    fn id() {
+
+        assert_eq!(
+            super::Descr::Git{url:"foo", branch:"bar"}.id(),
+            "424130b9e6c1675c983b4b97579877e16d8a6377e4fe10970e6d210811c3b7ac",
+        )
+    }
+//}
diff --git a/src/origin/descr.rs b/src/origin/descr.rs
new file mode 100644
index 0000000..32964a0
--- /dev/null
+++ b/src/origin/descr.rs
@@ -0,0 +1,45 @@
+use sha2::{Sha256, Digest};
+use hex::ToHex;
+
+/// A unique description of an origin, from where a domain might be served.
+pub enum Descr<'a> {
+    Git{url: &'a str, branch: &'a str},
+}
+
+impl<'a> Descr<'a> {
+
+    /// Returns a globally unique string for the Descr.
+    pub fn id(&'a self) -> String {
+
+        let mut h = Sha256::new();
+
+        let mut h_update = |b: &str| {
+            h.update(b);
+            h.update("\n");
+        };
+
+        match self {
+            Descr::Git{url, branch} => {
+                h_update("git");
+                h_update(url);
+                h_update(branch);
+            }
+        }
+
+        h.finalize().encode_hex::<String>()
+    }
+}
+
+#[cfg(test)]
+mod descr_tests {
+
+    #[test]
+    fn id() {
+
+        assert_eq!(
+            super::Descr::Git{url:"foo", branch:"bar"}.id(),
+            "424130b9e6c1675c983b4b97579877e16d8a6377e4fe10970e6d210811c3b7ac",
+        )
+    }
+}
+