key-generator.core.clj

(ns key-generator.core
  (:import (java.security KeyPairGenerator Key)
           (java.util Base64)))

(def ^:private algorithm->key-type
  {:RS256 "RSA"
   :ES256 "EC"})

(def ^:private algorithm->key-size
  {:RS256 512
   :ES256 256})

(defn generate-key-pair
  "Generates a private/public key pair based on the specified cryptographic algorithm."
  [alg & {:keys [key-size]}]
  (let [alg-keyword (if (string? alg)
                      (keyword alg)
                      alg)
        key-size-final (or key-size
                           (algorithm->key-size alg-keyword))
        generator      (doto (->> alg-keyword
                                  (get algorithm->key-type)
                                  (KeyPairGenerator/getInstance))
                         (.initialize key-size-final))
        key-pair       (.generateKeyPair generator)]
    {:private-key (.getPrivate key-pair)
     :public-key  (.getPublic key-pair)}))

(defn- key->pem [^Key key]
  (let [header (if (= (.getFormat key) "X.509") "-----BEGIN PUBLIC KEY-----\n" "-----BEGIN PRIVATE KEY-----\n")
        footer (if (= (.getFormat key) "X.509") "\n-----END PUBLIC KEY-----" "\n-----END PRIVATE KEY-----")
        encoder (Base64/getMimeEncoder 64 (.getBytes "\n" "UTF-8"))
        encoded-key (.encodeToString encoder (.getEncoded key))]
    (str header encoded-key footer)))

(defn write-key-to-disk [filename key]
  (with-open [writer (clojure.java.io/writer filename)]
    (.write writer (key->pem key))))

(defn -main [& args]
  (let [[alg output-dir] args
        {key-size :key-size} (apply hash-map (drop 2 args))
        key-pair (generate-key-pair alg {:key-size key-size})]
    (write-key-to-disk (str output-dir "/private-key.txt") (:private-key key-pair))
    (write-key-to-disk (str output-dir "/public-key.txt") (:public-key key-pair))))

project.clj

(defproject key-generator "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "EPL-2.0 OR GPL-2.0-or-later WITH Classpath-exception-2.0"
            :url "https://www.eclipse.org/legal/epl-2.0/"}
  :dependencies [[org.clojure/clojure "1.11.1"]]
  :repl-options {:init-ns key-generator.core}
  :main ^:skip-aot key-generator.core)

openssl rsa -in .\private-key.txt -check
openssl rsa -pubin -in .\public-key.txt -text