Among the English monarchs, Charles I is the one who personally made the most active use of ciphers during the years of the English Civil War.
Charles' relation with Parliament became irreparable when, at the beginning of 1642, he broke into the Commons chamber at the head of armed guards in an attempt to arrest the five most intransigent members, only to find that the forewarned MPs had fled. On 10 January, Charles got out of London with Queen Henrietta-Maria and the three eldest children.
In February 1642, Henrietta-Maria, who was resented by the Puritan subjects by her Catholic connections and coercive attitude, sailed for Holland, ostensibly escorting her daughter Mary, who had been married to the son and heir of the Prince of Orange.
Even in the previous year, Henrietta-Maria was aware that her letters were particularly targeted for opening and had to ask the Venetian ambassador to forward her letter to her friend staying in France in the diplomatic bag. (Plowden p.196)
The King and the Queen had arranged a cipher for use during their separation. It appears that Henrietta-Maria advised Charles to use her cipher in writing to her during their separation and Charles made additions to the cipher.
The first cipher between the King and the Queen was of an old style with symbols as well as figures. The alphabet was expressed by figures or symbols and small words were expressed by a combination of figures and letters. Further, proper names were represented by pseudonyms. Particularly deceptive was the use of the names of the principal leaders of the opposite party such as Pym, Hampden, Essex, etc. for the King, the Queen, and their adherents (Green p.viii).
Charles and Henrietta-Maria were devoted to each other but it was the Queen who had the strong will. She intently read Charles' cipher letters and she also wrote long letters in cipher to Charles, in which she told him what he must do.
While in Holland, she tried to raise money and arms for the King. Princes Rupert and Maurice, sons of Charles' sister, Elizabeth of Bohemia, went over to join their uncle, with arms and ammunitions. The Prince of Orange did what he could to help the royalist cause despite disapproval of the States General.
In August 1642, Henrietta-Maria, troubled by another cipher used in another channel, wanted to force their cipher upon that channel.
As it happened, this letter was the last use of their first cipher of the old style (Green p.viii, 97-98).
From the letter of 24 August/4 September 1642, the Queen started using a new cipher, which mainly consisted of figures. (Green p.viii, 99).
About the same time, in August 1642, Charles raised an army in Nottingham. With the prospect of open war in sight, Henrietta-Maria planned to join the King with the money and arms she had raised in Holland.
Henrietta-Maria not only relied on use of a cipher but also thought of deception of the parliamentarians about her landing by not using one.
Thus forewarning the King, she wrote about wrong landing places for the eyes of the parliamentarians. Thereafter, about the time the first action of the Civil War took place at Edgehill in October 1642, the communications were cut out completely for some time. (Gregg p.377)
Finally, she sailed and landed on the Yorkshire coast in February 1643. In June Henrietta-Maria left York and proceeded to Newark upon the River Trent. She joined the King around Oxford on 13 July.
The cipher used in letters from Henrietta-Maria to Charles I during this period was a numerical cipher by which several consecutive numbers were assigned to the letters of the alphabet as follows.
Numbers 70 and 72 were used as nulls or insignificant letters. Higher numbers represented proper names and words such as 159 (Generall), 189 (the King), 219 (Queen), 269 (Rebells), 300 (Treat), and 324 (London) in generally alphabetical order (alphabetical as regards the initial only). Some high-frequency small words had special codes such as a2 (&), d3 (have), d4 (he), e2 (in), e3 (is), e4 (it), g1 (make), g4 (may), h3 (now), k1 (of), n5 (would), n8 (with), which also seem to be arranged generally alphabetically. (After writing the above, the present author found the cipher is described in Manuscripts of His Grace the Duke of Portland, Vol. I, p.xxv. There appear to be some differences from the above.)
Use of this cipher in print can be found in:
Charles I to Henrietta-Maria, 23 January 1643 (Manuscripts of His Grace the Duke of Portland);
Henrietta-Maria to Charles I, 16/26 January 1643, written just before the Queen sailed from Holland (in English) (First Report of the Royal Commission, p.4);
Charles I to Henrietta-Maria, 13 February 1643 (Letters of the Kings of England, p.341; King's Cabinet Opened p.39, XXXVIII) [This letter is listed here because of its timing. It contains a couple of code numbers not deciphered.]
Charles I to Henrietta-Maria, 2/12 March 1643 (Manuscripts of His Grace the Duke of Portland; Davys p.45)
Henrietta-Maria to Charles I, 26 April 1643, written from York (in English) (Sixth Report of the Royal Commission, p.219) (Internet Archive)
Henrietta-Maria to Charles I, 9 July 1643, written just before the Queen joined the King in Oxford (in French) (First Report of the Royal Commission)
The second cipher was also used between the Queen and the Earl of Newcastle (Green p.ix).
Charles I wrote to Newcastle in a different cipher in November 1643 (Rushworth (British History Online)). (The cipher in the electronic version appears to be mutilated. A look at the paper edition would allow one to supplement the following.)
Numbers 60-90 appear to be mostly nulls. There are also three-digit figures 110 and 123, which would represent some words.
Another cipher used in Charles I to Richard Browne in Paris on 31 January 1643 has been identified by Eric Sams in 'Solution to the cipher letter of Charles I to Sir Edw. Nicholas' (PDF). It has a more irregular assignment of letters.
The summer of 1643 saw the zenith of the royalist fortune but the campaign ended in rather a disappointment.
A letter from Nicholas to Ormonde, dated 18 April 1644, uses a cipher for some words (Calendar of the manuscripts of the Marquess of Ormonde, K.P., preserved at Kilkenny, p.75 (Internet Archive)), which allows conjectural partial reconstruction of the cipher. It also employs an irregular assignment (though some part around 42-45 may have a reverse alphabetical order). Higher numbers represents words and names: 115 (the), 116 (his), 199 (earl), 211 (Jermyn).
In 1644, Prince Rupert won a series of victories in the north. The cipher used between Charles and Prince Rupert was similar to the second cipher with Henrietta-Maria.
Numbers 81-90 appear to be nulls. Higher numbers represented words such as 106 (army), 241 (King), 261 (Lord), 354 (Prince Rupert), 384 (treate), and 421 (will). Special codes for high-frequency words are a1 (&), a4 (be), b1 (but), c2 (doe), c4(for), c5 (a), c5 (for), e2 (hath), e3(her), e5 (in), f1 (is), f2(it), k1 (of), k5 (put), n1 (to), n3 (the), n4 (this), p5 (with).
An example is Charles I to Prince Rupert, 25 June 1644 (First Report of the Royal Commission, p.5). This was written to relieve Prince Rupert's distrust of persons around the King such as Lord Digby.
On 2 July 1644, in attempting to relieve York under siege, Prince Rupert, thus far believed invincible, had a disastrous defeat at Marston Moor, leading to loss of the entire north for the Royalists. Thereafter, the royalist control was restricted to the southeast.
At the end of August, Rupert arrived at Bristol and soon received a new cipher from the King.
When the King wrote to Rupert on 11 October in cipher, desiring him to join him, probably this cipher was used.
The above cipher of June 1644 letter was also used in the next year in a letter from Digby to Prince Rupert on 27 April 1645 (Folger Shakespeare Library) and in a letter from Digby to Ormonde as late as 26 September 1645 (Carte, A Collection of Original Letters and Papers, vol.1, p.91-95).
In late 1644, there was an underhand attempt to capture Abbington, which was held by parliamentary Major-General Richard Browne (namesake of the royalist minister in Paris mentioned above). After some preliminary exchanges, Digby sent Browne a cipher in a letter of 1 December 1644. (Rushworth (British History Online))
The cipher consists of an enciphering table (in alphabetical order), a deciphering table (in numerical order as above), and some codes ranging from 60 (King) to 419 (Croyland). It is noteworthy that "0" is used as a code for "and" and "0.0" for "of".
The negotiations between Digby and Browne were soon broken off.
Henrietta-Maria, now pregnant, left Oxford in April 1644 and gave birth to a child in Exeter. On 30 May, she wrote a letter to the Prince of Orange about an alliance and a second marriage between the Houses of Stuart and Orange, that is, between the Prince of Wales and a daughter of the Prince of Orange, Louisa Henrietta. Dr Stephen Goffe, who had been chaplain of Lord Goring's regiment in the Dutch service, carried the letter (Gardiner vol. i, p.409).
The cipher used for Goffe's instructions was a very regular one (see another article).
Henrietta-Maria went over to France. Exhausted from the childbirth in Exeter and the travel, even the energetic Queen told in a letter to the King that she could not yet manage to write in cipher and would have to leave that to Henry Jermyn, her trusted secretary. Afterwards, Jermyn undertook deciphering of Charles' letters for the Queen because of her headache (Plowden p.253).
Henrietta-Maria took a further precaution. From this time, the business-parts of the Queen's letters were given entirely in cipher, without a single word in plaintext so as not to give a clue to the pages of figures. This third cipher of the royal couple was much more comprehensive than the second and included a large range of words and syllables. Numbers up to 80 represent single letters and nulls; numbers to 322 are for names of persons and places and numbers up to 574 represented frequent words. (Green p.ix-x, 263)
In July 1644, the Queen's master usher was arrested near Malmesbury, Wiltshire, by the parliamentarians and many letters from the King, Lord Digby, and others were captured. (One of 30 June from the King to the Queen expressed his rejoice in the safe delivery of their last child.) Since the intercepted letters were in the cipher of Lord Jermyn instead of that ordinarily employed in communications between the King and the Queen, their content was revealed to historians only in 1888 in Calendar of State Papers (Internet Archive p.xv, 313-319).
In the spring of 1645, Jermyn used the following cipher in reporting to Charles that the Queen could not write to him because of illness (First Report of the Royal Commission, p.7).
Abraham Cowley, one of the leading poets of seventeenth-century England, was secretary to Jermyn. He ciphered and deciphered with his own hand the greatest part of all the letters that passed between the King and the Queen (Wikipedia, Molloy).
Jermyn used the third cipher of the Queen in a correspondence which he carried on under the Queen's direction with Goffe (Green p.x).
Negotiations with Parliamentarians were held in Uxbridge. A letter from Edward Nicholas, secretary of state, to Charles I dated 5 February used a cipher in which 276=the and 225=of (thus, this cipher may be denoted THE=276).
The negotiations ended in deadlock in February 1645.
In March 1645, Charles sent a private cipher to Henrietta-Maria by a trusted bearer.
An example of the King's use of this private cipher is seen below.
This letter was to be published in King's Cabinet Opened but the cipher remained undeciphered.
This cipher was only used on very few occasions (Green p.x). A deciphered letter of Henrietta-Maria to Charles I, 2 April 1645 printed in Green would help decipher this.
In the spring of 1645, the parliamentarians formed the New Model Army. In May, Charles left Oxford with his nephews Rupert and Maurice for the summer campaign. Soon, Edward Nicholas wrote from Oxford that Oxford was threatened by converging armies of Fairfax and Cromwell. The cipher used in the letter was as follows.
Numbers 73-83 represented nulls. Higher numbers include code numbers for two series of generally alphabetically ordered words and syllables: 90(all)-314(your) and 325(army) to 511(way). This cipher may be denoted THE=281.
On 14 June 1645, the King's army had a crushing defeat at Naseby. Not only was the military loss immense, the King's cabinet taken by the parliamentarians revealed the King's most secret papers and letters between the King and the Queen. On 23 June, the House of Commons resolved:
Of some sixty letters captured, many had been already deciphered by the King or Queen (Hulme p.70).
In July, the letters were published by the parliamentarians in King's Cabinet Opened. Among others, the King's efforts to obtain money and arms from abroad and to make peace with the Irish Catholics came to light.
In October, Lord Digby was given the command of an enterprise to join forces with Montrose in Scotland but was defeated on 15 October at Sherburn and his papers were captured. Again, the House of Commons resolved:
The papers captured on this occasion would be published in March 1646 in Lord George Digby's Cabinet.
After the Battle of Naseby, Charles still used the same cipher in writing to Nicholas because that cipher was not lost in the battle.
Notwithstanding, Nicholas provided the King with a new cipher (THE=277), receipt of which the King acknowledged on 9 August 1945.
Consonants are each assigned three code numbers and vowels four. Numbers 10, 20, ..., 90 are nulls. Higher numbers include code numbers for two series of generally alphabetically ordered words and syllables: 84(ad)-320(who), 323(arm)-521(trickery). Apparently, some numbers between different initial letters were reserved undefined for later additions.
The cipher used by Henrietta-Maria to Charles in a letter of 22 September 1645 was as follows (reconstructed from a facsimile page from Secret Writing).
Higher numbers were for names such as 124(Angleterre), 164(Irelande), 165(irelandois) and high-frequency words such as 279(and), 283(able), 285(affaire), 385(is), 413(men), 439(our), 440(out), 441(on), 475(religion), 476(rebell). Henrietta-Maria wrote in French but the vocabulary of high-frequency words suggests the cipher was prepared for English. Henrietta-Maria used syllables such as "our" and "out" for spelling French words as "19 439 36 42(m-our-i-r)" and "10 440(t-out)". Indeed, the same cipher was used by Jermyn in writing in English to Lord Digby, Secretary of State.
Henrietta-Maria usually used French but would write in English when there was not enough time for enciphering.
It is noted that this cipher is different from the third cipher of the King and the Queen or the cipher used in a letter from Digby to Jermyn dated 25 May 1645, before Naseby.
Further, Jermyn used a separate cipher in a letter to another Secretary of State, Edward Nicholas. This cipher was not shared by Henrietta-Maria but was also used by a report from Goffe at the Hague, dated 21 January 1646. Its key was also for Prince Rupert and the Duke of Ormonde. (Secret Writing, Letters No. 65-80)
Ormonde appears to have sent a new cipher to Digby after Naseby.
Digby also mentioned his "new cipher" about the same time.
The cipher used between Rupert in Bristol and Nicholas in Oxford in July 1645 was something as follows.
Higher numbers include two series of generally alphabetical words and syllables: 98(are)-373(well), 427(army)-616(victual).
Probably, this is the one Nicholas sent after Naseby.
Charles made efforts to bring troops of the Irish Catholics through Marquis of Ormonde, Lord Lieutenant of Ireland. On the other hand, Charles secretly authorized the Earl of Glamorgan to make more concessions to the Irish Catholics. When the draft of the Glamorgan treaty was known at the beginning of 1646, fierce criticism compelled Charles to disavow the powers he had given to Glamorgan.
However, Charles continued to support Glamorgan. In a letter of 5 April 1646, he told in cipher "you cannot be but confident of my making good all instructions and promises to you and the Nuncio" (words in italics were in cipher). On 20 July, Charles gave further assurances in a wholly enciphered letter.
The cipher used in these letters was not ordinary numerical cipher. Each of the twenty-four letters of the alphabet was expressed by four simple strokes varied in length, slope and position.
According to tonybaloney, Glamorgan called this "myne owne characters" when he used it for hiding his knowledge of which he feared ill use. The key written by the King himself is reproduced in Pall Mall Magazine (1896) Vol.8 No. 34 p.256.
See another article for use of this cipher in Glamorgan's letter to Ormonde in 1645.
After the defeat of Naseby, the royalists' fortune declined steadily. Reinforcement from the Irish did not materialize.
In the spring of 1646, even the royalist stronghold Oxford was threatened and Charles thought of a desperate attempt.
At the time, Newark was under siege of the Scots. Charles wrote many letters from Oxford to Lord Belasyse [Bellasis], the governor of the town. Most were in his own handwriting and at least some were in cipher. The last one was sent in a man's belly. It was put in lead, which the messenger swallowed, lest he should be taken in attempting to pass the Scot's army. In a letter sent "by this Extraordinary way of Conveyance", Charles told the governor of his resolution to go to the Scots' camp.
Charles barely got out of Oxford and threw himself to the protection of the Scottish army near Newark. He had been seeking an alliance with the Scots in many cipher letters passed between the King and Montreuil, an envoy from Cardinal Mazarin (Clarendon, Vol. 4, p.179). After Naseby, Mazarin thought the Parliament got too powerful and sought reconciliation of the King and the Scots, who had been disillusioned by the English Parliament. However, the King soon found himself all but a prisoner in the hands of the Scots.
Charles was brought to Newcastle, where he talked with the Scots. He could maintain his correspondence with Henrietta-Maria by the good offices of the French envoy but he was surrounded by staunch Presbyterians.
Soon after he was brought to Newcastle, Charles sent letters on 2 June to the Queen, the Prince of Wales, and councillors in Paris. He told them to follow the direction he had given before his unfree condition and, in all things for which no direction had been given, to follow the orders of the Prince of Wales. He told them that this would be the last free direction from him and warned that, whatever communications were made in his name, such should not be heeded unless they were written in cipher in his own hand. (Godwin p.172-173)
Oxford surrendered on 10 June and his second son James, the Duke of York, was put under custody of the parliamentarians at St. James' Palace. The first phase of the Civil War was now over.
After the fall of Oxford, Charles still managed to send some letters from Newcastle to Nicholas. Since Nicholas had destroyed their cipher, a new cipher was used, in which 17, 18=r, 280=of, 360=to.
After Naseby, as early as 5 August 1645, the King had written to the Prince of Wales, aged 15, who was striving to rally the royalists in the West, that in case of danger of falling into the rebels' hands, he should go to France (Clarendon, Vol. 4, p.83). The counsels about the Prince, however, did not think France a good choice for fear of the influence of the French court and the indomitable mother. Thus, they sent to the King a letter in cipher expressing their concern (ibid. p.87).
The King wrote more letters to tell the Prince to go abroad in case of "danger of falling into the rebels' hands". However, the King's letter dated 7 December 1645 positively commanded the Prince to go to Denmark or some other country. The letter was, "as the rest", written in Lord Culpepper's cipher and deciphered by him and, after the Prince's perusal, was delivered again to Lord Culpepper to be secretly kept (ibid., p.119). (Lord Culpepper, along with Edward Hyde, was the King's trusted friend appointed to attend the Prince of Wales.) The Prince's counsels explained to the King it was not the time.
The Prince of Wales moved to the Scilly Isles in March 1646 and then to Jersey in April 1646. The Queen, considering that the Prince was yet in the ill-defended Scillies, had written a letter in cipher dated 5 April 1646 to Hyde, advising the Prince to go to Jersey, via France if necessary, but her true intention was to have the Prince in France (Clarendon, Vol. 4, p.185-187). Thereafter, the Queen sent her express commands that the Prince should be removed to France. It was in agreement with the King's wish (Plowden p.262). The King in Oxford, somehow considering the Prince was in France, sent a letter to the Prince dated 22 March 1646 to Lord Jermyn in Paris. The letter written in Jermyn's cipher was deciphered by Jermyn and forwarded to the Prince (Clarendon p.187).
The Prince was pressed by the Queen to join her in Paris and Lord Capel and Lord Culpepper, the Prince's councillors, were sent to Paris. According to Hyde, when Montreuil, the French envoy, returned to Paris, it was "pretended" that he had brought a letter from the King, which was deciphered by Jermyn, in which he said the Prince could not be safe anywhere but with the Queen, and Montreuil professed to have a message by word of mouth to the same purpose (Clarendon, Vol. 4, p.199, cf. p.213). Capel was not persuaded and the impatient Queen sent Jermyn, Digby, and others with Capel and Culpepper to Jersey. In the end, the Prince of Wales decided the matter and went over to France at the end of June.
At Newcastle, the difference between the Scots and the King turned out to be irreconcilable. Charles was determined never to concede on matters of conscience. Fearing that Prince Charles might make a concession out of concern for the safety of the King, he smuggled out a carefully coded message to three councillors, Jermyn, Culpeper, and John Ashburnham in Paris (represented by codes 385, 386, and 383, not in order) on July 22 and commanded them not to yield, no matter what danger was apprehended to his person. He even resigned himself to his fate as a martyr: "I have already cast up what I am like to suffer, which I shall meet (by the grace of God) with that constancy that befits me."
In the end, the Scots gave up on Charles. In January 1647, they handed the person of the King to commissioners of the English parliamentarians, who escorted the King south to Holdenby (Holemby).
Just before they set out on 3 February, Charles wrote in cipher to the Prince of Wales in France, telling him not to come to England, upon any persuasion or threatening, before he sent for him. The letter was intercepted and was deciphered by John Wallis. The cipher used was as follows (reconstructed from the facsimile printed in Geneva, Astrology and the Seventeenth Century Mind p.25).
In Holdenby, although Charles was allowed to walk or even ride, his correspondence with the outside ceased. He was not allowed to write or receive a letter from the Queen, his children, or friends and he was allowed to speak with anyone only in the presence of some of the commissioners (Colonel Joseph Bampfield's Apology, Sections 40, 41, Plowden p.269).
One day, when he was riding, a Major Bosvile [Bosville], entrusted with the task of conducting the King's secret correspondence (Hillier p.90), thrust into his hands a parcel containing letters from the Queen but it was detected and the man was sent away (Green p.337, Gregg p.412). A few weeks later, a woman, perhaps Jane Whorwood, visited Charles at Holdenby. Searching her did not produce anything but afterwards a letter in cipher was found behind the hangings where she had stood in Charles' room. Watch on Charles was tightened after these events. (Gregg p.412)
Another such episode concerns a Mungo Murrey, who was a confidential servant and gentleman of the bedchamber to the King and was often entrusted with the King's private correspondence. In February 1647, when Murrey was admitted to the King's presence before witnesses, the commissioners saw something put into his hand by the King. He was searched afterwards and a letter in cipher directed to Montreuil was found. Murrey was held in prison for two days. (Evelyn's Memoirs, Vol. 5, p.54)
In May 1647, the Commissioners discovered a letter in cipher to be delivered to the King by a Mary Cave and forwarded it to the Parliament. The letter was written on the back of a petition, merely a cover for the ciphers, brought by John Browne, servant to Ashburnham. Upon examination, Browne admitted that he received the letter from Ashburnham, then at the Hague. (Lords Journal)
According to Colonel Bampfield's own account, the barber placed by the Parliament was won over and he provided means for conveying letters unperceivably into Charles' hands when he served the King every morning and evening (Apology, Section 40).
Meanwhile, disagreement grew between Parliament and the army. In June, the army under Oliver Cromwell and Thomas Fairfax took over the King's person. Charles was moved to Hampton Court. Though he enjoyed some freedom and received visitors including his children, he was closely watched. He could write letters but he had little communication with the Queen (cf. Gregg p.417, Plowden p.270, Clarendon, Vol. 4, p.525, Green p.337).
In this period, an Anthony Jackson reported the King's feeling towards Nicholas from Hampton Court in a letter dated 6 September 1647. The cipher is preserved in Egerton MS 2550, f.5, endorsed by Nicholas "My second cipher with the King, Aug. 1647." (Nicholas Papers, p.87-88)
In November, Charles escaped from Hampton Court and went to the Isle of Wight, believing that the Governor was sympathetic to the royalist cause. His expectation was wrong and he soon found himself all but a prisoner in Carisbrooke Castle. He had attendants and had visitors but the parliamentarians took care that only those with their permission could visit him (Hillier, Carlton). All his correspondence was blocked again. A messenger, sent by Bosville, trying to deliver a packet of letters to Mrs. Wheeler or her maid Mary was caught and the packet was found to contain a letter from the Queen and one from the Duke of York (then in the hands of the parliamentarians) among others (Hillier p.91 ff.). The Queen's letter was mostly written in the queen's "cabalry and mystical lock of numbers" and no one could read them. (Plowden p.271)
Charles had still some friends. A laundry woman Mary Wheeler undertook to conceal arriving letters under the carpet or behind the wall hangings. But when an escape plot in February was discovered, Mary and other assistants were sent away. (Gregg p.422, Carlton ) Mrs Dowcett, the wife of the kitchen clerk, smuggled out letters to the Queen (Carlton ).
Henry Firebrace, the King's one-time page, managed to ingratiate himself into the favor of one of the King's conservators and obtained a duty of waiting at the door while the King absented himself at supper and thus had occasions to talk to the King when he retired to his chamber. In order to avoid being seen with the King, a chink was made in the wainscot behind the hangings. By this means, they could talk and exchange notes for making arrangements for his escape plan (Hillier p.100, 105, 112; Carlton). They arranged some letter codes for names such as: A (Cresset), C (Col. Legge), F (Dowcett), Z (Mr. Worsley) (Hillier p.112).
One day, Charles caught the governor of the Isle, Robert Hammond, searching his room and he barely succeeded in throwing his papers into the fire.
In March, the plot prepared by Firebrace and Captain Silus Titus, one of the conservators appointed by the Parliament but won over to the King's side, was abandoned at the last minute (Gregg p.422, Carlton p.323, Hillier p.108ff.). The plan was known to the Parliament and Titus and Firebrace were dismissed in April (Hillier p.116, 122). After the failure of the attempt to escape, Charles obtained from supporters files and nitric acid to cut the bars of the window when playing bowls (Carlton p.324, Hillier p.130ff.). But before the plan was carried out, Charles was moved to different quarters in the castle (Carlton p.324, Hillier).
Charles still found means to smuggle out letters (Hillier p.144). In letters to Titus, a numerical cipher was used in addition to the above-mentioned letter codes. Lower numbers were reserved for single letters.
Further, it had two series of generally alphabetically ordered words and syllables such as 103(am)-420(you) and 453(business)-608(trouble), followed by numerals such as 634(one), 647(twenty), days and months such as 659(Monday), 665(Sunday), 672(May) and some random words such as 680(wife), 686(escape), and 705(boat).
Charles also wrote to his son James, the Duke of York, held in custody under the parliamentarians in St. James' Palace. However, James' reply in cipher was intercepted by the parliamentarians (see another article) and he was examined by a committee. The fourteen-year-old prince learned a lesson.
On the other hand, the King continued writing letters. Charles believed that his cipher would not be broken and his disguised handwriting would not be recognized. (Carlton p.325, Poynting p.130)
Soon there was a new development. By the beginning of May, the whole of South Wales was in revolt against Parliament, marking the start of the second phase of the Civil War. In April, the Duke of York succeeded in escaping from St James' Palace and went over to the Continent. About the same time, some English ships came over to the royalist cause. Upon hearing this, Prince Charles went from Paris to Calais and took over the control of the small fleet.
When the King found out whereabouts of the Prince, he wrote on 1 August partly in a cipher, which had been sent to the Prince "by the noble friend who conveys this letter to you from me". In the letter, Charles told his son to act by the advice of the council, to "be constant to those grounds of religion and honour", and to write letters to him.
A cipher letter for Prince Charles dated Newport, 3 October 1648 can be found in Vindication, p.158
An attempt to escape at the end of May again ended in failure, leading to a tighter security. (Carlton p.324)
For some time, Charles thought all means of communication with the outside was cut off. However, by the assistance of a humble woman who served in his room, correspondence with Titus and other friends was recovered in July (Hillier p.239, 243, Poynting).
Colonel William Hopkins, a resident of Newport, located in the center of the Isle, undertook to forward his letters to his friends in London or abroad. In correspondence, Charles and Hopkins discussed "Great Business", using a cipher and disguised handwriting -- what Charles called 'slow hand', a neat secretary script rather than his normal italic (Poynting p.130).
This cipher, however, was for concealing only some proper names. Thus, an astute reader might penetrate into the meaning of a message such as: "unless you secure 50 the Seizing of all the rest of the Horse, will not (in my Opinion) do the Work; because he will sooner get Help to recover his Loss, than you be able to force 39 out of his hands" (Charles I to Hopkins, 16 July 1648).
The known code numbers used in correspondence with Hopkins are as follows (Vindication)
39 Charles I
54 "some considerable Officer under Hammond, who had a mind to be honest"
57 Mrs. Wheeler
60 "fresh Souldiers sent into the Isle"
N. Mrs. Whorwood
Occasionally, they added code numbers they used.
Charles wrote on 3 August to Hopkins that he had a visit from Jane Whorwood and he might give her full confidence. Soon, a cipher "N" was assigned to her. (This is the same letter code as Charles used with Titus, with whom he afterwards used a numerical code 715 (Hillier p.143, 147).) He was even ready to disclose to her the cipher he used with Hopkins.
Jane Whorwood was an ardent supporter of the royalist cause and she procured files and nitric acid and had money smuggled to the King by the assistance of Mrs Dowcett. Some says she was his mistress but the exact nature of their relationship is not known for sure. By July, she was in the Isle of Wight.
While the cipher with Hopkins was only for some names, Charles used a more extensive cipher with Jane. Two of Charles' letters to Jane in this cipher are extant (see Poynting).
In a letter of 24 July, Charles advised her how she could secretly visit him: first getting acquaintance with the new woman who could be trusted and getting into the stool room in his bedchamber by her assistance while he is at dinner, they would be able to have three hours when he would be alone after dinner every day. In the second extant letter of 26 July, Charles proposed another plan for her to invite herself to dinner at Captain Mildmay's chamber next to his, where he would surprise her and get her alone into his chamber.
As noted above, Jane did visit the King on 3 August but he had no time to speak to her. In the evening of 28 August, she again stole a visit upon the King, who could scarcely believe his eyes when he saw her (Charles I to Hopkins, 29 August 1648).
The second civil war was short but resulted in much bloodshed. The capitulation of Colchester in August marked the end of the war in the Eastern counties. The Scots were crushed at Preston by Cromwell in the same month.
Horrified at the bloodshed, the parliamentarians offered to renew the negotiations with the King and in early September Charles was allowed to leave Carisbrooke Castle to stay at Hopkins' house in Newport and his advisers were allowed to join him.
An extant letter written in the hand of Jane (back in London) and signed with a pseudonym "Hellen" (printed in Vindication) is of especial interest in that the cipher has been deciphered by the King himself. This letter allows partial reconstruction of the cipher, with which the above letters of 24 and 26 July have been deciphered.
This is more irregular than the cipher with the Queen or Ministers. Higher numbers are, as usual, words in roughly alphabetical order from 72(army) to 386(your) plus further additions such as 389(Jane), 391(Charles), and 422(escape).
The letter of "Hellen" warned of "a notable design, to which are agreed the Army and Parliament ... to dispose of his Majesty" and provided some advice about escape. However, in mid-November, an escape plan was detected almost as soon as it was designed.
As late as Novenber 1648, Nicholas was in touch with the King. Finding that the King did not have Ormonde's cipher the latter believed he had, Nicholas sent a copy to the King.
The army feared that agreement of Parliament and the King might nullify their military victory. Ironically, it was Charles' one-time gaoler Hammond who refused orders from the army to imprison Charles without written orders from Parliament. He was recalled and arrested by the army. In December, Charles was seized by the army and taken to Hurst Castle. He managed to take his ciphers with him.
In Westminster, on 6 December 1648, Colonel Pride purged from Parliament many members who were not supporters of the army. This sealed Charles' fate. The remaining members of the Rump Parliament put the King on trial for treason and condemned him to death. On the morning of the 29 January, the King burnt his papers, including the keys of his ciphered correspondence (Gardiner p.319). On 30 January 1649, Charles was beheaded.
Charles used many ciphers with various correspondents, including those not mentioned above. The variety of his ciphers in a way reflects his troubled years.
Letters of the Kings of England (1848) (Internet Arcihve)
Charles I. in 1646: Letters of King Charles the First to Queen Henrietta Maria (Internet Archive, Google Booksearch)
Manuscripts of His Grace the Duke of Portland, Vol. I (Internet Archive)
The King's Cabinet Opened, in The Harleian miscellany, Vol. 5, p.514 (Google Booksearch); the original edition at Google
Green (ed), Letters of Queen Henrietta Maria (1857) (Internet Archive)
English Civil War Regiment of Lord Molyneux and civil war battles...Letters of Henrietta-Maria
Memoirs of Prince Rupert, and the cavaliers (Google)
Memoirs of John Evelyn, Esq. F.R.S., Vol. 5 (Google)
Report of the Royal Commission on Historical Manuscripts (some volumes are found online: 1; 3; 4; 6; 7; 8; 10; 12; 13; 14; 15; 16; 17; 18)
Secret Writing in the Public Records, Public Record Office (1974)
Letters between Col. Robert Hammond, Governor of the Isle of Wight, and the Committee of Lords and Commons at Derby-House (1764) (PDF)
A vindication of King Charles the Martyr (1711), p.140 ff. Appendix (Google Booksearch)
George Hillier, A Narrative of the Attempted Escapes of Charles the First from Carisbrook Castle (1852) (Google)
Rushworth, John, Historical Collections of Private Passages of State (1721) (British History Online)
Carte, A Collection of Original Letters and Papers, Concerning the Affairs of England, from the Year 1641 to 1660, Found amond the Duke of Ormonde's Papers (vol.1, vol.2)
Carte, The life of James duke of Ormond (Internet Archive)
Gregg, Pauline, King Charles I (1984) (plain text structured text)
Carlton, Charles, Charles First, the personal monarch
Plowden, Alison, Henrietta Maria, Charles I's Indomitable Queen
Godwin, William, History of the Commonwealth of England: To the death of Charles I (1826) (Google Booksearch)
Earl of Clarendon, The History of the Rebellion and Civil Wars (Google: Vol. I, Vol. II, Vol. III, Vol. IV, Vol. V, Vol. VI, Vol. VII) (Internet Archive: Vol. I, Part 1, Vol. I, Part 2, Vol. II, Part 1, Vol. II, Part 2, Vol. III, Part 1, Vol. III, Part 2)
Gardiner, History of the Great Civil War, 3 vols.
Marshall, Alan, Intelligence and Espionage in the Reign of Charles II, 1660-1685
Jason Peacey, 'The Exploitation of Captured Royal Correspondence and Anglo-Scottish Relations in the British Civil Wars 1645-46', The Scottish Historical Review, LXXIX, 2: No.208: October 2000, 213-232
Poynting, Sarah, 'Deciphering the King: Charles I's Letters to Jane Whorwood' (a free summary is found here)
Eric Sams, 'Solution to the cipher letter of Charles I to Sir Edw. Nicholas' (PDF)
John Davys, An Essay on the Art of Decyphering (1737)
Hulme, F. Edward, Cryptography (Internet Archive)
Birch, Thomas, An inquiry into the share: which King Charles I. had in the transactions of the Earl of Glamorgan (1756) p.360, 242 ff. (Google Booksearch)
Hallam, Henry, The constitutional history of England from the accession of Henry VII. to the Death of George II. (1832) p.264 (Google Booksearch)