201212231409 15cd8y

solved decrypted manual

'Merry Christmas'. 3DES-CBC, key MD5(name), IV presumed.

Metadata

Post ID: 15cd8y
Title: 201212231409 → 2012-12-23 14:09 on A858's clock
Posted (UTC): 2012-12-23 22:09:05
Timezone: UTC−8 · title 14:09 against posted 22:09 UTC
Author: [deleted]
Account: A858DE45F56D9BC9 main account
Subreddit: r/A858DE45F56D9BC9 the main subreddit
Category: S solved special
Content: Seasonal greetings and ASCII art
Size: 32 hex characters · 16 bytes
Cipher: 3DES-EDE2 (two-key Triple DES), CBC, PKCS7
Key: MD5(A858DE45F56D9BC9) = 34a14a42e98ff96095af56604e290cae (name)
IV: CF40AD098EC6A4A8 presumed: the IV was never published, so it is derived from a guessed first block (see the steps below)
Sources: community-archive, arctic-shift · body from community-archive
Links: Reddit · Arctic Shift · JSON
Score · comments: 23 · 15
Tags: automated (decryptable)2012Solved special postmanualeditedkey: nameseasonal greetings and ascii art

F8E2417DCC2CC99C 9E1804CF1A268158

Other archived version (the post was edited)

0000000000000000

Derive the key. Password = A858DE45F56D9BC9 (name); key = MD5(password) = 34a14a42e98ff96095af56604e290cae, used as a two-key 3DES key.
Decrypt. 3DES-EDE2 in CBC mode, then strip the PKCS7 padding.
Presumed IV. The IV was never published. Assuming the first 8 bytes are "Merry Ch", the IV is D(C0) XOR that block = CF40AD098EC6A4A8. A presumed value, not a recovered one: every block after the first decrypts the same way whatever the IV is.

Merry Christmas

Status: verified against the archived post.

The body is whitespace-separated hexadecimal. Decode it to ciphertext, then decrypt with two-key 3DES (DES-EDE-CBC):

The plaintext is:

Merry Christmas