201309131459 1mby18

explained decrypted filler

seed 751

Metadata

Post ID: 1mby18
Title: 201309131459 → 2013-09-13 14:59 on A858's clock
Posted (UTC): 2013-09-13 18:59:59
Timezone: UTC−4 · title 14:59 against posted 18:59 UTC
Author: [deleted]
Account: A858DE45F56D9BC9 main account
Subreddit: r/A858DE45F56D9BC9 the main subreddit
Category: F3 filler: 3DES(name/title) → GUID list, seed known
Size: 272 hex characters · 136 bytes
Cipher: 3DES-EDE2 (two-key Triple DES), ECB, PKCS7
Key: MD5(A858DE45F56D9BC9201309131459) = 6dd5ed6e0ddbbe000bb1a34825d499ac (name+title)
GUIDs: 4
Filler GUID seed: new Random(751).Next(9) ✓ verified
Run: Run 53 (seed 26,950,390) (seed)
Draw: 26 · predicted N = 4 ✓
Machine boot: 2013-09-12 09:30–10:30 (seed = uptime at app start)
Sources: community-archive, arctic-shift · body from community-archive
Links: Reddit · Arctic Shift · JSON
Score · comments: 5 · 0
Tags: automated (decryptable)2013Encrypted masked GUID listkey: name+titlerun: seed

From the post to its content

As posted (encrypted)

3CD57525E98CAC69 42EB5F8D95E67AE3 F0AADDD05FD49D43 756C4958044ACF39 3C2A8A257E7F13D7 2BC87DA836EF6DAB F938BE7D4BA278EA 5C97936F5FCEF6DE 5479557ED7772ED0 B0B6F7A61B6FAE4E BE6F5AA7C1FC171C B9E9DEA97CE739D0 255EB85E485BEF8D 90905254BD1F1D4D E2555B5E3B7CC9BA 2AA25846FC9F9F8E D418AAEF090C3B50

Read the ciphertext. Strip whitespace: 272 hex characters = 136 bytes = 17 8-byte 3DES blocks.
Derive the key. Password = A858DE45F56D9BC9201309131459 (name+title). Key = MD5(password) = 6dd5ed6e0ddbbe000bb1a34825d499ac, used as a two-key 3DES key.
Decrypt. 3DES-EDE2 in ECB mode, then strip the PKCS7 padding. The plaintext is 4 GUIDs as hex (shown below).

Decrypted: GUID list

  1 fd54d467-f88e-0d31-9ea2-aa092fc5f280
  2 b9900a9e-15e6-15dd-8810-e9f88e66966f
  3 7819be6e-8655-6c1f-a99c-4356c60928aa
  4 15a45aa4-15cf-7059-a2cb-a49f821c0f2f

Explanation

Explain the mask digits. The version nibble (13th hex digit) of each GUID, read in order, gives 0167. Exactly this sequence comes out of new Random(751).Next(9): the per-post millisecond seed of the mask generator. The other 30 hex digits of each GUID are Guid.NewGuid() output and carry no message.
Explain the count. This post is draw 26 of Run 53 (seed 26,950,390): new Random(26950390), 4·Next(1,12) per post. The RNG predicts N = 4; the post has N = 4 ✓. The seed is the machine's uptime in ms when the app started (boot 2013-09-12 09:30–10:30).
Conclusion. Filler. The content is fully explained by the two RNGs.

Metadata

From the post to its content

As posted (encrypted)

Decrypted: GUID list

Explanation

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