Medieval Security Techniques

Sonja Drummer describes (with photographs) two medieval security techniques. The first is a for authentication: a document has been cut in half with an irregular pattern, so that the two halves can be brought together to prove authenticity. The second is for integrity: hashed lines written above and below a block of text ensure that no one can add additional text at a later date.

Posted on February 12, 2021 at 2:05 PM22 Comments


Me February 12, 2021 1:30 PM

I liked how she pointed out that the second technique is what we still (some of us anyway) do for checks, just scribbling out the rest of the area.

vas pup February 12, 2021 1:48 PM

The first one was used (in some movies)to guarantee payment when cash notes were cut in half, and one half was given to the person before action requested, and second half – after action was done. So, both parts have their leverage and desire to complete transaction.

I have no idea is it possible to get the whole note in the US bank when only half of it is brought to the bank. Probably depends on central bank rules in particular country.

JonKnowsNothing February 12, 2021 2:45 PM

@vas pup

re: Exchanging damaged bank notes for good ones in the USA

If you have the pieces, scotch tape works pretty well until you can take it to a bank for exchange or pass it along to someone else in a transaction, or even just deposit it to an account. If you have the majority of the bill the bank will exchange it for a new one (ripped corner).

US bank notes have some unique identifiers on them and if the note is severely damaged (fire, flood, moth-rat-mold eaten, shredded etc), a bank will sent the pile of bits to the US Treasury for recovery. They select whatever unique identifier they can find on the remnants for counting. They will then return that amount in undamaged notes.

Some unique parts: The Seal, Face Parts (eyes), The Key, Building Landmarks and of course, the serial numbers. They can even use the corners which are different.

ht tps://$100_Federal_Reserve_Note.jpg

ht tps://
(url fractured to prevent autorun)

Clive Robinson February 12, 2021 5:37 PM

The second method we used to call a variation of as “Zeding out”.

That is you drew a line under the last of the text from the left side of the page to the right then diagonaly back down to the bottom left corner where you continued with a line along the bottom to the bottom right corner. You would then turn the page clockwise so the diaginal line is horizontal and sign along it, and add the date.

And if your signiture is as comprehensible as a drunken spider track you would using block capitals print your name below the now horizontal diagonal line. Also if required add a reason or scope of the ‘zeded’ close out. Such as “End of page 3”, “End of §5” etc. Some people would add strike throughs at the begining and end of this signiture and reason (indicating they were working by wrote rather than reason).

But there was another method used and is still used on “Papul Bulls” and similar.

A slot is cut right through the page under the writing end and a second about half an inch below. Then a thread, cord or ribon put through the string cord or ribbon would be held in place with a hot wax seal or a compressed soft metal seal made of lead or gold etc.

The seal is called a “bulla” and was a logical follow on from clay tokens used for four thousand years or so for trade accounting.

Such hardened/fired tokens would, to form a contract, be put inside a wet clay ball the details pressed onto the outer surface and then dried/fired.

In effect it formed a binding contract that could if challenged be verified by withesses. The clay ball examined then broken open and the contained tokens then examined.

The ingenuity of such systems increased with mankinds ability not just to encode / impress / modulate information onto matter but also the general understanding of why such systems could be trusted.

However some such systems reach a point of utility where going further decreases the security of a given system, or worse trying to transfer the idea from one physical domain to another domain that is not entirely physical etc.

Something most had forgoton untill all the dirty little secrets of “improved” voting machines eventually showed they are anything but more secure.

xcv February 12, 2021 6:55 PM

I’m banned from Twitter with HTML5 and Flash supercookies, and I cannot even view Twitter links without tails, Tor, or something like that.

rusty chicken beaks February 12, 2021 10:26 PM

@ xcv:

I cannot even view Twitter links without tails, Tor,

That would require you to enable javascript on either choice, which is generally discouraged!

or something like that.

Something like that? You either use TAILS and/or Tor Browser or you don’t, there is no “something like that” to it.

Epi-curious February 12, 2021 11:25 PM

If it were “easy” to forge (re-write) the text on a new piece of paper (parchment) surely it wouldn’t be difficult to repeat the cut on the left by using the original as a template (the cut in the picture does not look very sophisticated). What am I missing?

MrC February 13, 2021 12:42 AM

@ Clive:
The “bulla” sounds similar to the dying practice among old-fashioned Anglo-American lawyers of “ribboning” or “tying” a last will & testament. The pages are bound with a red ribbon and fancy knotwork, then the ribbon is run through slits in the back of the signature page and covered with a seal. A disappointed heir cannot add or substitute a forged page granting themselves a larger inheritance without removing the ribbon, which can’t be replaced absent the ability to forge the seal too. Here’s a video example shot on a camera with roughly the same resolution as a potato: HyperTextTransportProtocolSecureColonSlashSlash

lurker February 13, 2021 12:54 AM

@Epi-curious: in the version I had previously seen the paper was raggedy torn by hand, much harder to forge a matching half. The similar and older Chinese version used a stone or ceramic tablet which was broken in two pieces: no way to spoof a match with the technology of that era.

Clive Robinson February 13, 2021 3:29 AM

@ MrC,

Here’s a video example shot on a camera with roughly the same resolution as a potato

And a “Old Beethoven mic” as well 😉

But yes that is the time honoured process, and also why the same “pink ribbon” is still seen on legal briefs and the like.

It was a job that usually fell on “law clerks” who back in earlier times were actually trained not just in law but the priesthood as well.

In fact at one point to qualify from certain universities you were expected if not required to take up “orders”.

Thankfully times have changed and the holding of a D.Law, D.Phil, or D.Div or equivalent does not require you “to kneel down and grip the cloth” as a friend used to less than politely describe it.

SpaceLifeForm February 13, 2021 12:52 PM

@ Clive, MrC, rusty chicken beaks

There is a lot of misdirection happening.

Keep that in mind.

See my last on prior squid. Still last.

Still no response.

It was almost a Strawman, but the attack was missing at the end.

vas pup February 13, 2021 2:22 PM

Thank you for Your input! VP
I looked at $100 bill and found out you can’t cut it in half so only one part have #. Both will have.
Anyway that is good technique to confirm credentials of somebody. Each contacted person will have unique number on their own part/half of the bill.

Johannes February 14, 2021 2:38 AM

Others have described this in comments as well, but here is a more in-detail list of letterlocking techniques:

From the site: “Though recently coined, the term letterlocking describes an old and varied practice, that of using one or several of a suite of physical methods to ensure that nobody reads your letter but its intended recipient — and if someone else does read it, to show that they have.”

So it’s essentially medieval AEAD.

Drone February 14, 2021 11:00 AM

@Schneier said: “Sonja Drummer describes (with photographs) two medieval security techniques.” First, it’s Sonja “Drimmer”, not “Drummer”. Second, if you are going to post a link to a Twitter post, add a warning about Twitter CENSORSHIP based on ideology.

Drone February 14, 2021 12:27 PM

@Johannes: Thanks for the link. However, the first YouTube video “Letterlocking: Mary Queen of Scots’ last letter, a spiral lock, England (1587)” is deeply flawed. The letterlocking technique shown is completely reversible and can be easily reapplied once an unauthorized interloper has read the letter. Also, the white tool shown (typically made of bone, whale baleen, or ivory) is entirely wrong for the letterlock being demonstrated. The correct tool will be flat to aid in creasing and it will also have a hook on the end like a knitting needle. This hooked tool is commonly used by traditional bookbinders to crease groups of ordered pages into a folded “signature” which is then added to a sewn “stack”. The hook is used to grab the binding thread and pull it out between the signatures in the growing stack. In letterlocking the lock “tail” is passed through the folded letter and usually knotted, then the hook is used to grab the lock tail and drag it inside the folded letter. This makes the letterlock very difficult to open without causing telltale damage. Letterlocks are by no means robust. A common practice would be to use a letterlock fold then enclose the locked letter in an envelope sealed with a unique wax (meh) or tree resin (better) seal.

Cryptic February 14, 2021 10:15 PM


Thankfully times have changed and the holding of a D.Law, D.Phil, or D.Div or equivalent does not require you “to kneel down and grip the cloth” as a friend used to less than politely describe it.

although this ‘process’ is evermore required by all applicants to MI15, M16, CIA, FBI, NSA as a demonstration of fealty, subservience and disavowal of their pesronal will

Stephen Mason February 15, 2021 6:38 AM

An old technique. I cover this in my open source book: Electronic Signatures in Law (4th edn, Institute of Advanced Legal Studies for the SAS Humanities Digital Library, School of Advanced Study, University of London, 2016)

Donald Eastlake February 15, 2021 6:54 PM

On the ancient dividing of a document into parts that can be authenticated by fitting back together, this is well known and the source of the word “indenture”, which today just means an important legal agreement. Originally, grants of land and the like were called “deeds”, as they are now, but there were two types: a “deed indenture” and a “deed poll”. A deed indenture was written in duplicate on one piece of parchment, both copies were signed, and they were cut apart along a wavy line producing two originals that would fit back together. Hence each original had a side that was “indented”. If the sides of a solemn document were straight, it implied only one original existed and you had a “deed poll”, “straight” being an archaic meaning of the word “poll”.

xcv February 16, 2021 7:06 PM

The first is a for authentication: a document has been cut in half with an irregular pattern, so that the two halves can be brought together to prove authenticity.

Bearer bonds, promissory notes etc. to be matched up and checked off at the time of redemption. There was a British government official, the “chancellor of the exchequer” or something like that.

The second is for integrity: hashed lines written above and below a block of text ensure that no one can add additional text at a later date.

And that was the purpose behind the closely set Gothic blackletter text with flush margins, typical of medieval Europe.

xcv February 24, 2021 7:21 PM

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