From 42f619457d58e3c34237d7d3fe55d5bb19a2ba90 Mon Sep 17 00:00:00 2001
From: Andrew Cady <d@jerkface.net>
Date: Sun, 31 May 2020 20:30:53 -0400
Subject: "hostname.cryptonomic.net" shows the cryptonomic hostname of the
 current system

---
 src/hostname.cryptonomic.net | 43 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100755 src/hostname.cryptonomic.net

diff --git a/src/hostname.cryptonomic.net b/src/hostname.cryptonomic.net
new file mode 100755
index 0000000..913948a
--- /dev/null
+++ b/src/hostname.cryptonomic.net
@@ -0,0 +1,43 @@
+#!/bin/dash
+
+die() { echo "$0: Error: $*" >&2; exit 1; }
+
+DEFAULT_PEM_FILE=/etc/ssh/ssh_host_rsa_key.pub
+if [ "$1" = -h ]
+then
+    cat >&2 <<EOF
+Usage: $0 [pem-file]
+
+    Default pem-file is $DEFAULT_PEM_FILE
+EOF
+    exit
+fi
+
+b16_to_b32()
+{
+    echo -n "$1" | basez -x -d | basez -j -l | tr -d =
+}
+
+pem_to_host()
+{
+    local INPUT="$1"
+    DNS_FMT=$(ssh-keygen -r . -f "$INPUT")
+    HEX_FMT=$(echo -n "$DNS_FMT" | sed -ne 's/^. IN SSHFP [0-9]* 2 //p')
+    B32_FMT=$(b16_to_b32 "$HEX_FMT")
+
+    read keytype keydata < "${INPUT}" || die "reading from INPUT=$INPUT"
+    case "$keytype" in
+        ssh-rsa|ssh-dss|ecdsa-sha2-nistp256|ssh-ed25519)
+            domain=$keytype.cryptonomic.net ;;
+        *)
+            die "Unsupported key type: $keytype" ;;
+    esac
+#   echo $HEX_FMT.$domain
+    echo $B32_FMT.$domain
+}
+
+INPUT=${1:-$DEFAULT_PEM_FILE}
+[ -f "$INPUT" ] || die "not a file: $INPUT"
+
+pem_to_host "$INPUT"
+
-- 
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