Ciphers in Early Stuart England before the Civil War

In the early seventeenth century, ciphers that use figures rather than arbitrary symbols (see another article) became popular in England but symbols were still used in early years.


Isaac Wake's Numerical Cipher (1619, 1628)

Isaac Wake, British representative at Turin (Wikipedia), used a numerical cipher in his correspondence with the secretary of state.

Figures followed by an alphabetic letter are codes such as 87.b (Venetians) and 54.c (ambassadors).

He provided the same cipher to Thomas Roe at Constantinople and started to use it in March 1628.

Wake to Roe, 30 March 1628 NS (Roe's Negotiations p.787; another example is on p.801)
Your lordship, I hope, hath receaued a paper of auvisi secreti, which I sent unto you three months since. In conformity unto that aduertisment, I will now tell your lordship, that I haue understood, from a uery good hand, that 91.a (the emperor) hath, of late instantly moued 68.b (the state of Venice) with him against 49 (t) 21 (h) 12 (e) 64 (-) 50 (t) 51 (u) 45 (r) 28 ([k]) 13 ([e]) 70 (-) 69 (-). ...

Wake used the same cipher with his correspondence with the King of Denmark (in Latin) (Roe's Negotiations p.788).

Calvert-Roe(-Buckingham) Cipher (1622-1624)

The cipher used in letters between George Calvert, Secretary of State, and Thomas Roe, ambassador to Constantinople, involves not only numerical code for names and titles but also a substitution alphabet of eight letters a, c, e, n, r, s, t, u. As it turned out, each letter of the alphabet is represented by a pair of letters according to the checkerboard arrangement below. The key for the substitution is presented by tonybaloney. It is probably the same as "Secretary Calvert's cipher" used between Roe and Lord High Admiral Buckingham in State Papers Foreign, Ciphers (SP106) 4, no. 28. (Secret Writing, Nos. 51, 52), which the present author has not seen.

The cipher was intended for use between Calvert and Roe but Roe also used it in writing to Buckingham.

Roe to Calvert, 14/24 December 1622 (Roe's Negotiations p.113)
I must confess, I committed an ill manners of necessity, to vse your cyphar to my lord admirall, which I must now againe borrow (Secret Writing No. 51 is the deciphered letter to the Lord Admiral of the same date): but fearing that therefore your honor may forbeare, supposing I had written secretts of that kind therein, I may disaduantage myselfe, if I did not signify, that they couer only a priuat pretious busines; and I am bold to referre his lordship to you for the other.

In the checkerboard above, the plaintext letters are arranged regularly but the cipher letters at the head of rows and columns provide irregularity. The arrangement could be memorized as a Latin phrase "nunc tua res" (now your thing). Other key words could be arranged to change the substitution pattern, though no such use is known to the present author.

It is apparent that this particular key word has a flaw in that it assigns the same letter "n" to both the first row and the third row. This must have posed considerable trouble for codebreakers (and even for intended recipients).

Of the code numbers, some can be identified from known deciphering of a letter from Calvert to Roe dated 1 October 1624 (Roe's Negotiations, p.292-293): 151 (the grand signor), 89 (the kyng of Spayne), 179 ([Venetian] ambassador), 156 (Constantinople).

The above key, albeit defective, allows (for the most part) reading of undeciphered letters in Roe's Negotiations

Roe to Lord High Admiral Buckingham, [2]0 November 1622 (Roe's Negotiations p.107; another letter on p.27 on the same topic is also said to be in cipher and is mentioned on p.54 on the same thread)

That your lordship requires the modell of the cucanuurcrnr (diamon), I haue long since sent it by my kinsman, wherein I doubt not you are satisfied in the proportion. The truecanutu (price) cannott be beaten, vntill they know wee are prepared to uutens (buy): thus much I am assured, it will be two thirds vnder the cetuuecananatu (teriffe) of catunstunrnrtuuene (jewellers); and by coniecture, I think, wilbe bought about 30000 trcrtenreune (pounds), which is not 500 the nunuueuetuce (carret): and for a catunstunr (jewel), in that trtuuenatunucecacrnr (perfection), I think it is not deare. There is no hope nor good to be done in uununrnrnunutune (ballaces); here are great plenty to sell, and of exceeding magnitude. Nothing wilbe taken but urcrnrns (mony), nor can it euery day be had, nor in my power to keep it, if any other meanes to putt it off. As yett it is safe, and not come abroad; whensoeuer it doth, if I be not prouided by creditt, it is lost for euer; such commodities issue out of the nuerteuece (court) from the nserurtunr (women) in great secrecy, and in their necessity. Therefore, if either his majestie or your lordship haue a resolution to uutens (buy) this or any other, you must furnish mee with creditt, and trust to my judgment and discretion: I am not altogether ignorant in this art, and will doe nothing but very warrantably. For trtunuuenrtune (pearles), here is one of 100 nunuueuetucene (carrets), of good forme, and I think, the greatest in the world, that is faire; but it is held equall, or not much vnder the truecanutu (price) of the cucanuurcrnr (diamon). But if your lordship desire any of these, I can prouide you at very good rates, either uecrtenrcu (round) or trtunrcutunrce (pendent) from 6. to 30. nunuueuetucene (carrets), in perfection; butt these also are offered sodainly in the same manner, and I must be furnished to take them when the seller needes. I would have aduentured vpon a cucanuurcrnr (diamon) for your lordship, if Iliad bene able; it is an nununrnatu ([h]alfe) uauecrtenrcu (ground) nececrnrtu (stone), the cenuuunrtu (table), as greate as that of Sir P.P. but cenacunrnrtu (th[e]nne), of exceeding showe and perfection, about 16 nunuueuetucene (carrets); the truecanutu (price), 5 or 6000 l. when money, scene perhaps easier. If your lordship take any resolution, I humbly desire a speedy answere and order; for I must lay hold of opportunity offered, or not attall.
That his majesties letter could not bring a false alarum, that he replyed, (as is said) That this was not the nacauenece (first) nrnstu (lye); the merchants had made him nsuecacetu (write) nuuuuecrnucu (abroad); other things were only repetitions of familiar conferences betweene his majestie and him, warning him to take heed of the merchaunts, for that they were deuills...

Roe to Calvert, 10/20 February 1622 [i.e., 1623 in the modern calendar] (Roe's Negotiations p.129)

I mentioned in my last an Nuuatcnrec (ag[e]nt) arriued from 102. There is come in his company a Nunutrcenunsurtu (Captay[n]e) and a Nauenunrnucanenununr nauccatuue (Franciscan frier), that hath bene cenauetutu censurtune (three tymes) in the like uutenecanrtune (busynes) employed. Hee keepes himself in Netunutenrnunt nanuuucace (secula[r] habit), except among those of his owne coate. Hee hath brought hither nenrnutetune (slaues) and other truetunetunreene (presents) in name from the uauenunrcu cutenunutunenc (grand duccess), mother of 202, and hath instructions to treate somewhat secretly: hee pretends some ouerture of a commerce betweene that state and this port; but wee know that the foundation of the cruecutuue (order) of nenrce necetutrnanrcr (ALt AtepFLo???) will, nor can admitt; it therefore that, wee are assured, is a colour. The 179 ([Venetian] ambassador) and 180 are very ielous, that hee treates a peace for 88. The vizier told mee, That an offer was made priuatly; but named not the instruments. I am sure I know as much thereof as any, and can as yet assure nothing but this; 5 hee hath busines to treate, and bringes not truetunetunrcens (present[s]), for noe end my opinion is, That hee is sent from Nrnutrnrtuns (Napley), and passed by 210, and mett 183 vppon the way. His negotiation is for 102, yf it goe noe further; and that 88 haue noe interest therein.

Roe's Negotiations further presents on p.57 an undeciphered passage "truecanrnutunacanrcauutuuece" in a letter to Calvert 17/27 June 1622, which can be deciphered as "Prince Filibert". On p.141 is Roe's letter to Calvert on 5 April 1623, which includes "unnuncncuu of nuuauccanu", which appears to be garbled (possibly in transcription).

A similar checkerboard cipher is preserved in the collection of ciphers for the reign of Charles I, though it is improved in that each letter can be represented in two (or three for "a") ways. It is said to have been used for correspondence with Flanders and France but no examples are found among the state papers calendered in the Domestic Series (Calendar of State Papers, Domestic series, of the reign of Charles I, 1645-1647 (Internet Archive) (1891) , p.viii).

Lord Carew against Use of Cipher

On the other hand, Lord Carew, Privy Councillor, was against use of cipher.

Lord Carew to Roe, 8 December 1623 (Roe's Negotiations, p.200)
Your lordship may remember, that in one of your former (to prevent the danger of miscarrying of letters) you wished that a cipher might passe betweene vs; against which proposition I gave many reasons to the contrary, the somme whereof is, that if any of ours were intercepted, and written in a composed character, it would drawe suspition and jealousie vppon vs, although the contents were of no moment; and farther, in the same letter, I did pray your lordship to excuse me for not writinge any matter worthy your view....

Roe-Conway Cipher (1625-1627)

Correspondence between Roe (in Constantinople) and the other secretary of state Conway began in 1624 and a cipher was established early in 1625 (Roe's Negotiations, p.271, 309, 355). It employs simple substitution scheme representing the letters of the alphabet by figures 2-9, with "1" used as a null or a word break. Since each figure represents three letters, distinction had to be made by writing a dot or a ditto-like sign or cross over the figure.

Code is also used. So, for example, the sequence of figures 7943576262 must somehow be parsed as "794(for) 3(a) 57(peace) 6262(with)", with "57" referring to the code (Roe's Negotiations, p.461).

17 England
20 the king (of Great-Brittayny)
21 his majestie
24 the king of Bohemia
42 Constantinople
57 peace
59 treaty
60 league
61 allies
64 letters
66 warr
70 ministers
71 ambassador(s)
72 agent
90 France
91 the French king

101 the emperor
106 the house of Austria
107 Vienna
115 Germans
116 Bohemia
119 Morauia
120 Silesia
124 Hungary
125 Hungarians
127 Bethlem Gabor
128 Transilvania
130 the prince of Transilvania
131 Moldavia
133 Styria
134 Carinthia
137 Wallachia
140 Poland
141 the king of Poland
144 the Cossacks
152 Sweden
153 the king of Sweden
154 the grand signor
174 the Turks
175 Turkish
178 Christendome
199 Tartars
203 the Muscovites
207 French ambassador
208 Venice ambassador
214 the ambassadors resident
234 Venice
235 the state of Venice
241 the duke of Savoy
257 the Low Countries
258 the States

Conway-Wake Cipher (1626)

A cipher used in a letter of Secretary Conway to Sir Isaac Wake, dated 6 December 1626, is in State Papers Foreign, Ciphers (SP106) 4, no. 33 (Secret Writing No.53), which I have not seen.

Roe-Elizabeth Cipher (1626)

Here is an interesting reenactment video titled "Elizabeth Stuart Deciphering Sir Thomas Roe's Letter: Cryptography, 1626". It shows a cipher used in Roe's letter to Elizabeth, Queen of Bohemia. Roe (c.1581-1644) had been devoted to Elizabeth (1596-1662) since her infancy (Roe's Negotiations p.59; Wikipedia) and was concerned about the fate of her and her husband, King of Bohemia, who had been ousted from his realm in 1620 and, deprived even of his Palatinate estates, compelled to seek refuge at The Hague in 1621.

The nomenclature appears to be a usual figure code including 8/9 (nulls), 14 (his Majesty), 201 (Hungary), 204 (Transylvania), and 205 (The Prince of Transylvania).

Each of the 24 letters of the alphabet (with no distinction between i and j as well as between u and v, as was common at the time) is represented by a combination of two symbols like "nκ" for "a", "07" for "b", "px" for "c", etc. The first symbol appears to be a letter shifted by 12 places in the alphabet (i.e., Caesar cipher), making the second character redundant, unlike the checkerboard scheme such as the Calvert-Roe Cipher and Roe-Conway Cipher above.

Cipher of Frederick V, King of Bohemia, and Elizabeth, Queen of Bohemia (1622, 1631-1632)

In 1622, Frederick V, King of Bohemia and consort of James I's eldest daughter Elizabeth, shared a code with William Trumbull, an English envoy in Brussels (Akkerman p.1055, 1056, "Key Frederick V").

From late 1631 to early 1632, the same code was used by Frederick and Sir Henry Vane, both staying near the Swedish army in the Palatinate, in their correspondence with Elizabeth, Queen of Bohemia and also by Sir Balthazar Gerbier, Trumbull's successor in Brussels (Akkerman p.1055). The Code had been partially reconstructed by M.A. Green (Elizabeth, Electress Palatine and Queen of Bohemia (Internet Archive), p.291) (116 (Charles I), 140 (Prince d'Orange), 129 (Duc de Saxe), 149 (General Vere), 165 (La Haye), 170 (Sir Henry Vane), 181 (Ambassadeur), 192 (Argent), 199 (Armée), 214 (Duc de Simmern)) and was further reconstructed by Akkerman by using Trumbull's copy (Akkerman p.1056). After the death of Frederick in 1632, the Queen initiated her son Charles Louis with the same code (Akkerman p.1055).


Gerbier-Elizabeth Ciphers (1631-1640)

In addition to Frederick V's cipher, Sir Balthazar Gerbier, an English resident agent in Brussels, designed ciphers for Elizabeth (Akkerman p.1055, "Key 1 Gerbier" and "Key 2 Gerbier").

Gerbier's first cipher, used from December 1631 to at least December 1638, represents each letter of the alphabet typically by a figure or letters. For example, "k" is represented by "r", "80", or "81" and "y" is represented by "9", "dd", or "hh". (Such mixed substitution alphabet is also seen in Spanish ciphers.) The nomenclature part used symbols as well as figures. Thus, the King of Spain is represented by "117" but the King of France is represented by a symbol.

("9" represents "the King" in the nomenclature and "y" in the substitution. Presumably, the correspondents could tell whether a number refers to the substitution or the nomenclature because similar numbers should occur one after another in substitution.)

Gerbier also shared this cipher with Sir John Coke, secretary of state, and Lord Treasurer Weston. A cipher between Gerbier and the other secretary of state Windebank around 1639 is mentioned in notes to No. 62 of Secret Writing.

Gerbier's second cipher was used from March 1636 to at least April 1640.

Gerbier's letters to Charles I (14 December 1631, 4 September 1638) partly in cipher are printed (only in decipherment) as No.60 and No.61 in Secret Writing.

Roe-Elizabeth Ciphers (1636-1642)

Elizabeth, Queen of Bohemia, sent her two sons, Charles Louis and Prince Rupert, to the English court in February 1636 and was trying to persuade her brother Charles I to help the cause of Charles Louis, Elector Palatine.

Thomas Roe designed ciphers for Elizabeth (Akkerman p.1055, 1056, "Key 1 Roe", "Key 2 Roe", and "Key 3 Roe").

The first cipher was used from 1636 to 1638. In July 1636, Roe sent a cipher to Elizabeth, because "there may be cause for secrecy." (Cal. SP, Domestic, 1636-37, pp.69-71, 83) Two days after receiving it, Elizabeth used it for trial (ibid. pp.94, 125), saying she wrote in cipher that he might see if she understood it right, adding that she hoped he might read it, for it was terribly scribbled (Elizabeth to Roe, 17/27 September 1636).

This had a feature that baffled Elizabeth, who had years of experience in corresponding in cipher. While the nomenclature was nothing special, with figures and capital letters representing names and words, the substitution was a polyalphabetic version of simple Caesar cipher, in which the number preceding a cipher (as in "4ri") specified the alphabet to use. That is, if the key number is 4, the letter "a" is aligned with "d" (i.e., the 4th letter in the alphabet) in the Caesar-style substitution pairing. After all, Roe suggested to Elizabeth not to use the substitution alphabet but only the nomenclature. Roe discarded the polyalphabetic system in the subsequent ciphers.

Roe's second cipher for Elizabeth was short-lived and was used from September 1638 to November 1638.

Roe's third cipher was used as late as 1642. In 1641-1642, Roe also used cipher with the Queen's son Charles Louis, Elector Palatine. (Cal. SP 1641-43)

Cave-Elizabeth Cipher (1638)

Elizabeth, Queen of Bohemia, had a cipher with her London-based agent, Sir Richard Cave (Akkerman p.1055, "Key Cave"). The substitution alphabet was to assign two to four figures to each letter of the alphabet in regular arrangement, somewhat like Viscount Scudamore's cipher below. Possibly for use in German, it uses "21" with an overline and "22" with an overline to represent "ss". In the nomenclature, numbers up to 20 were used as nulls and higher numbers represented names such as 84 (the King of England) and 261 (Cave).

Wentworth-Charles I Cipher

King Charles I is known to have used various codes and ciphers during the English Civil War (see another article). But Charles I's use of cipher dates back further than that.

The following is the cipher used between Charles I and Thomas Wentworth (1593-1641), appointed Lord Deputy of Ireland in 1632 and later created 1st Earl of Strafford in 1640.

Higher numbers were used as code numbers representing words or names such as 111,112(Th), 121/122(the), and 185(Earl of St Albans).

Wentworth-Laud Cipher

Besides the King, Wentworth used cipher most commonly in letters to William Laud, Archbishop of Canterbury (1633-1645). Cipher was regularly used in "great letters" between Wentworth and Laud (Merritt p.94), two principal advisers of the King after the assassination of Buckingham in 1628.

The following is the cipher used between them.

Again, higher numbers represented code numbers such as 85/86(the), 102(Laud), 110(the Exchequer), and 171(Dublin). Numbers less than 30 are nulls, which were used as deceptions or word divisions. (Different aspects of this cipher were described by Eric Sams and Ralph Weber, who mentioned the substitution cipher and the code portion, respectively.)

It was Wentworth who brought cipher into their correspondence, to the puzzlement of Laud.

I have received your cipher, but God in heaven knows what I shall make of it. If you write much in it, it is impossible I should find leisure to sit and decipher it. If you write only five or six lines, which you would keep secret, it may be I may make a shift to read so much; though I am such a stranger to that course, that I cannot tell whether I can or no. But if I cannot, I'll tell you so.
Laud to Wentworth, 13 January 1633 [i.e., 1634] (Works, vol.7, p.60)

When he received a letter including a few lines in cipher, Laud decided not to try to read them till he was "at better ease and more leisure". Afterwards, he "made a shift with the three passages" and even wrote a marginal note in cipher (Laud to Wentworth, 12 April 1634; Works, vol.7, p.68, p.70). His incorrect enciphering, however, ended up in puzzling Wentworth, to the glee of Laud.

Next comes in your complaint of the cipher in the margin of my letter. O how it pleases me to see you hampered in your own cords. If I had leisure, I would stay and solace myself with this just revenge of your troubling me with a cipher, that have lived thus long without any in my life, or from my pen.
And it joys me more because there was no malice in it, but mere chance, for I protest I did nothing purposely; and it doth me good, too, that it was in a place which you did most desired to know. And, which makes the revenge full, I keep no copies of my letters I send you, for want of time, and so cannot repair it, but leave you in that ignorance.
Laud to Wentworth, 23 June 1634 (Works, vol.7, p.76)

When Wentworth wrote a long passage in cipher, Laud preferred "less cipher", saying "the length I could bear with, but so much in cipher I am not hold out with, being necessary to be deciphered by myself, no other being trusted, and considering my years and employment" (Laud to Wentworth, 30 November 1635).

When a trusty messenger was available, they could dispense with use of cipher. William Raylton, Wentworth's agent in London, occasionally travelled between London and Ireland to convey sensitive information not to be committed to paper. Thus, Laud, whom he regularly met, remarked in July 1635, "I am glad that William Raylton saves us the trouble of a cipher." In the same month, Lord Goring wrote he would trust with Raylton "some of our dayly passages which I think not soe fitt to trust this and such like withall especially since the late perusal of papers as they pass at home and abroad." (Merritt p.124)

At one time, Laud was concerned that the cipher table they possessed would allow their letters to be read when they were dead and proposed to burn the letters between them (Laud to Wentworth, 3 August 1635; Works, vol.7, p.166). This was not approved by Wentworth but Laud decided to take more care by deciphering in another paper rather than between the lines and burning it after writing an answer (Laud to Wentworth, 4 October 1635; Works, vol.7, p.180).

In April 1637, Laud proposed to add some numbers in the cipher.

You see by this we have frequent use of more Lords' names than are in our cipher, ergo I pray add to it (for I have done it already) 177 for my Lord of Northumberland, 178 for Earl of Dorset, 179 for Earl of Leicester, and 180 for the Lord Ashton.
Laud to Wentworth, 5 April 1637, Works p.337

Wentworth in turn proposed in a letter received on 14 September 181 for France and 182 for Spain (Works p.364). During the following months, they went on adding numbers up to 202 for Earl of Berkshire, being added on 31 March 1639 (Works, p.550; see the also list on xxiv).

Wentworth was recalled to England in September 1639, when trouble with Scotland was brewing.

Roe-Laud Cipher (1638)

Laud also used cipher in writing to Thomas Roe, now appointed as ambassador in Hamburg (Laud to Roe, 19 July 1638, Works p.459). He had asked Roe to use cipher only for a name or two (Laud to Roe, 5 July 1638, Works p.458) and now observed "your cipher is extreme hard, and, by your leave, ill expressed. And if I had had time to revise it before your going I would not have endured it as it is; therefore, I pray, overload me not with it. As for the false writing from 80 to 90, that's nothing; for so long as your paper is so as well as mine, it comes all to one; therefore I shall not alter that."

Roe had also sent a cipher to Elizabeth, Queen of Bohemia in the Hague, in July 1636, saying "there may be cause for secrecy" (see above).

Wentworth-Windebank Cipher

The cipher for use between Wentworth and his friend, Sir Francis Windebank was as follows.

Cipher for Viscount Scudamore, Ambassador in Paris (1636)

A cipher used in 1636 by Viscount Scudamore, ambassador in Paris, is presented by tonybaloney. His letter to secretary Windebank of a near date (11/21 July 1636) is found in Cal. SP Domestic, p.59-60.

This assigns three or six figures to each letter of the alphabet, not unlike the Cave-Elizabeth Cipher (1638) above and the Ormonde-Clanricarde cipher (1643) (see another article), though it is somewhat better in that the regular arrangement of the alphabet is randomly interrupted by nulls.

Cipher between Secretary Windebank and His Son (1640)

The British Library website has images of a letter from Secretary Francis Windebank to his son, Thomas, from 1640. The following is a partially reconstructed cipher.

Windebank's use of cipher with Robert Read (Thomas' cousin) on 26 May 1644 is known (Cal. SP, Domestic, 1644, p.171 (Internet Archive)). Read also used cipher with Thomas in 1641 (Cal. SP, Domestic, 1640-1641, p.506 etc. (Internet Archive)).


Cipher used by Secretaries of State

Many other letters in cipher are known. In 1628, George Henry in Ireland sent a cipher to Secretary Coke. The cipher consisted of a "list of figures to be used to denote the names of the principal noblemen and gentlemen of Ireland". (Cal. SP, Domestic, Charles I, p.113)

When Charles I travelled north in May 1633 for coronation in Scotland, Secretary Windebank sent a cipher to Lord Treasurer Portland, who was with the King, by direction of Lord Cottington. (Cal. SP, Domestic, Charles I, p.76) (Portland and Cottington were a pro-Spanish group in the council, to whom Laud was bitterly opposed. Windebank owed his appointment in the previous year partially to Laud but more to the influence of Portland and Cottington (RBH Biography).)

The following letters written partially in cipher are printed in abstract and/or decipherment in Calendar of State Papers and Secret Writing.

Secretary Coke, who had been in office since 1625, resigned and was succeeded by Sir Harry Vane in February 1640. Vane took over the seals with the ciphers. From this time, the two secretaries of state were responsible for different regions: Windebank for Spain, Flanders, and Italy and Vane for France, Holland, Germany, and the Baltic states. Roe, who had sent a long proposition in cipher, was notified that he would receive an answer from Windebank but in future Vane was responsible for the correspondence with him. (Calendar of State Papers, Domestic, Charles I, p.433, 434)

In late 1641, Windebank and Vane left office and Edward Nicholas took over the correspondence with Roe (Cal. SP, Domestic, p.193). Use of cipher in some of their letters in 1642 is recorded (ibid.).


The negotiations of Sir Thomas Roe, in his Embassy to the Ottoman Porte (1740) (Roe's Negotiations herein) (Google)

Nadine Akkerman (ed.), The Correspondence of Elizabeth Stuart, Queen of Bohemia, Volume II (2011) (Google)

Notes on Ciphers Used in Stafford Correspondence, Papers of Thomas Wentworth

The works of the Most Reverend Father in God, William Laud, vol.7 (Internet Archive, Google)

J. F. Merritt, The Political World of Thomas Wentworth, Earl of Strafford, 1621-1641

Calendar of State Papers, Domestic Series (A volume is not specified in the above citations but may be tracked from the date.)

Sheila R. Richards (ed.), Secret Writing in the Public Records, Public Record Office (1974)

Eric Sams, Cracking the Historical Codes

Ralph E. Weber, United States Diplomatic Codes and Ciphers 1775-1938, pp.13-14

©2010 S.Tomokiyo
First posted on 25 July 2010 under the title "Strafford's Ciphers", then expanded under the title "Ciphers during the Early Reign of Charles I before the Civil War". Further expanded and renamed on 18 April 2015. Last modified on 15 October 2016.
Articles on Historical Cryptography
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