Decrypting Civil War Messages..

Over the holiday break an interesting story broke on a US Civil War message being finally decrypted after 147 years. The message was in a bottle that had been stored in a Virginia museum since 1896, but had never been investigated. Finally in 2010 a curious collections manager, Catherine Wright asked retired CIA codebreaker David Gaddy to crack it and see what it said.

The story of the message is interesting in itself, but what I wanted to share with you is how obscure the craft of codebreaking can be. Let’s start with a picture of the message so you know what we are dealing with here…

Encrypted message to Gen John Pemberton, 1863

Now, the first stage of decryption is of course to read the actual message itself, which as you can see due to the damage (and penmanship) is pretty hard – I solicited a smart person to help me read it and this is what we came up with.

STAN WITUIIUZH ORO ONP LBNXOK OZ HJQB FEQT FEQT XZBW JJOA
TK EHR FPZWK PBW RYSQ VOWPZXGG QEOH BK WASEKIPW PLVO
JKZ NMN NIAEVO XVE DWAJ BOYPA SK VLD TYVROE LVPL.
MTYSIN XY FQEO NPK M OBPC FYXJFHONT AS ETOV B OCAJOSVQU
U ZTZV TPJY DAW RQTI WTTJ. J DQGOAIA FLWHTXTH QMTR STA LVLPLXTO

Now, luckily I know the right key to this message, so imagining I was the guy who received it back in 1863, I thought I’d give it a go decrypting it..

gtnl pebberton jmc oan exvekt no nelp frok bmxn gyqc eeca
gi xdz mlivz vwr fyfo okewvgfv wzjv bx utomreyv erqj
xkm lfj vpwnud dqz rwnh ukgww bj kry omvemx hdwh.
vsnydi ly soxk vwg v nqvx amxwdakva wb diuq w ccnhhodxq
d yifq odjl bts zxpr vize. e rqtmtei mhfgidoc emgp lpi sruoadoj

Obviously something has gone very wrong indeed here. The first part of the text is mildly readable – you could infer it says “Genl Pemberton, ??? can expect no help from ???? ???…” then it gets totally messed up.

A hint can be found in the original ciphertext on the first line – you can see the code word “FEQT” is repeated. Now, this is VERY unlikely using the Vigenere cipher, so maybe it’s an accidental duplicate – maybe the person drafting the message wrote the same word twice by mistake?

Let’s try again after deleting this extra codeword and see what we get:

gtnl pebberton jmc oan exvekt no nelp frok this sidg
of she diver lkv genl jojnston mnnw hf rosrible when
yqu ian agtadv ted scve polnt os chm snbmjs line.
ibform me also and i will endeavoar to make a divecsion
q have sept yow eome eaps. i swbjoin despatcg fsom gtn johxstcn

This is much better – we can infer a lot from this, in fact the end of the message makes a lot of sense:

“Inform me also, and I will endeavorer to make a diversion. I have sent you some caps. I subjoin dispatch from Gen Johnson”.

You can see how vital it is to properly encrypt messages to start with – our poor interpretation of the original makes the bulk of this message unintelligible.

Digging around and playing with my interpretation of the letters, it’s possible to get the actual intended cipher and plaintext back, which for posterity is:

SEAN WIEUIIUZH DTG CNP LBHXGK OZ BJQB FEQT XZBW JJOY
TK FHR TPZWK PVU RYSQ VOUPZXGG OEPH CK UASFKIPW PLVO
JIZ HMN NVAEUD XYF DURJ BOVPA SF MLV FYYRDE LVPL.
MFYSIN XY FQEO NPK M OBPC FYXJFHOHT AS ETOV B OCAJDSVQU
M ZTZV TPHY DAU FQTI UTTJ. J DOGOAIA FLWHTXTI QLTR SEA LVLFLXFO

Genl Pemberton you can expect no help from this side
of the river let Genl Johnston know if possible when
you can attack the same point on the enemys line
inform me also and I will endeavour to make a diversion
I have sent you some caps I subjoin despatch from Gen Johnston

The lesson of this blog of course is, if you have to hand-encrypt something:

1. Make sure you write legibly

2. Double check you didn’t make any mistakes before sending your message out!

Tags: Civil War, enterprise, Pemberton

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