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diff --git a/src/block.rs b/src/block.rs
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+//! # Data Representations
+//!
+//! We need persistence for [`Block`]s and [`User`]s, not so much for [`Transaction`]s
+//!
+//! There are around 30 students, a full fledged database would be an overkill (for next year?)
+//!
+//! Pending transactions are held in memory, these are cleared with every new block
+//! Only the last block is held in memory, every block is written to a file
+//! Users are held in memory and they're also backed up to text files
+use chrono::{NaiveDate, NaiveDateTime};
+use serde::{Deserialize, Serialize};
+use std::{string::String, vec::Vec};
+
+pub type Fingerprint = String;
+pub type Id = String;
+
+/// A block that was proposed with `transaction_list` and `nonce`
+/// that made `hash` valid, 6 zeroes at the left hand side of the hash (24 bytes)
+///
+/// We are mining using blake2s algorithm, which produces 256 bit hashes.
+/// Hash/second is roughly 20x10^3.
+///
+/// <https://serde.rs/container-attrs.html> might be valuable to normalize the
+/// serialize/deserialize conventions as these will be hashed
+///
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
+pub struct Block {
+    #[serde(skip_serializing_if = "Vec::is_empty")]
+    pub transaction_list: Vec<Fingerprint>,
+    pub nonce: u32,
+    pub timestamp: NaiveDateTime,
+    pub hash: String,
+}
+
+impl Default for Block {
+    fn default() -> Self {
+        Block {
+            transaction_list: vec!["gradecoin_bank".to_owned()],
+            nonce: 0,
+            timestamp: NaiveDate::from_ymd(2022, 4, 11).and_hms(20, 45, 00),
+            hash: String::from("not_actually_mined"),
+        }
+    }
+}
+
+/// For prototyping and letting serde handle everything json
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
+pub struct NakedBlock {
+    #[serde(skip_serializing_if = "Vec::is_empty", default)]
+    pub transaction_list: Vec<Fingerprint>,
+    pub nonce: u32,
+    pub timestamp: NaiveDateTime,
+}
+
+/// A transaction between `source` and `target` that moves `amount`
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq)]
+pub struct Transaction {
+    pub source: Fingerprint,
+    pub target: Fingerprint,
+    pub amount: u16,
+    pub timestamp: NaiveDateTime,
+}
+
+/// A JWT Payload/Claims representation
+///
+/// <https://tools.ietf.org/html/rfc7519#section-4.1>
+///
+/// - `tha`: Transaction Hash, String (custom field)
+/// - `iat`: Issued At, Unix Time, epoch
+/// - `exp`: Expiration Time, epoch
+#[derive(Debug, Serialize, Deserialize, PartialEq)]
+pub struct Claims {
+    pub tha: String,
+    pub iat: usize,
+    pub exp: usize,
+}
+
+/// The plaintext of the initial user authentication request
+#[derive(Serialize, Deserialize, Debug, PartialEq)]
+pub struct AuthRequest {
+    pub student_id: String,
+    pub passwd: String,
+    pub public_key: String,
+}
+
+/// Ciphertext of the initial authentication request, or what we will receive
+#[derive(Serialize, Deserialize, Debug)]
+pub struct InitialAuthRequest {
+    pub c: String,
+    pub iv: String,
+    pub key: String,
+}