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These puzzles have been set by the experts at GCHQ. The difficulty levels are gauged using the Enigma Rotor Scale, which you can find described at https://www.gchq.gov.uk/information/enigma-rotor-scale

  1. Very easy. Should be quickly solvable. 
  2. Not too hard but not immediately obvious. You probably need to make a cup of tea for this one. Coffee works too. 
  3. Getting a bit hard now. Tea drinking will help, but a bit of pacing around the room is probably in order as well. 
  4. Something of a meaty challenge and probably one you might need to collaborate with other people to solve. 
  5. Very difficult and time consuming. There might well be multiple answers. But, then again, maybe there‚Äôs just one answer. 
  6. At this level it might be far from obvious even what the question is asking, never mind how you might go about solving it.  Good luck!

  • GCHQ Puzzle Solution 17

    Last but not least

    What are the missing three terms in this sequence

    AAEH, EKKJ, HMLN, MRUO, ?, ?, ?

    The answer this week is provided by Kfford-Academy:

    T, T, W. This is very much like Challenge 16, with the four disciples Matthew, Mark, Luke and John. Here is how to get the sequence:

    Step 1 – Reorder the letters of each term in alphabetical order:
    matthew -> aehmttw
    mark -> akmr
    luke -> eklu
    john -> hjno

    Step 2 – Put these new terms into a grid, as follows:
    aehmttw, akmr, eklu, hjno
    |
    v
    aehmttw
    akmr
    eklu
    hjno

    Step 3 – Read off the columns:
    aehmttw
    akmr
    eklu
    hjno
    |
    v
    aaeh, ekkj, hmln, mruo, t, t, w

    This is the last of our GCHQ puzzle challenges for now but we hope to be back with more like this soon. Enjoy …

  • GCHQ Puzzle Challenge 17

    Last but not least

    What are the missing three terms in this sequence

    AAEH, EKKJ, HMLN, MRUO, ?, ?, ?

    (The answer is not ?, ?, ?)

    This is the last of our GCHQ puzzle challenges for now but we hope to be back with more like this soon. Enjoy …

  • GCHQ Puzzle Solution 16

    A good way to start the week?

    You were asked to find the missing four terms in this sequence

    AAAAAAA, DDDDDDA, NMEDHFD, SNSERIR, UOTESRS, ?, ?, ?, ?

    The solution is:

    YYUNTYT, YSUU, WYY, Y.

    Did you work it out? It was very tricky. The fact that there were seven items in the list, together with the puzzle title might have suggested that it had something to do with the days of the week, and it does.

    The sequence is derived by writing the letters of each day of the week in alphabetical order then reading the answers off by columns.

  • GCHQ Puzzle Challenge 16 – Harry’s Hint

    A good way to start the week?

    What are the missing four terms in this sequence

    AAAAAAA, DDDDDDA, NMEDHFD, SNSERIR, UOTESRS, ?, ?, ?, ?

    (The answer is not ?, ?, ?, ?)

    I am not sure what to tell you about this one, but maybe you need to think laterally. It is another one where the number of items in the list might be suggestive.

  • GCHQ Puzzle Challenge 16

    A good way to start the week?

    What are the missing four terms in this sequence

    AAAAAAA, DDDDDDA, NMEDHFD, SNSERIR, UOTESRS, ?, ?, ?, ?

    (The answer is not ?, ?, ?, ?)

  • GCHQ Puzzle Solution 15

    Capital letters

    What is the only possible way to complete this sequence?

    CCR, CR, SV, RBT

    The answer is NCS for Nicosia.

    Each sequence is the sequence of consonants from the capital of a country whose name contains only one vowel:

    CCR from Accra, the capital of GhAnA

    CR from Cairo, the capital of Egypt

    SV from Suva, the capital of FIjI

    RBT from Rabat, the capital of MOrOccO

    NCS from Nicosia, the capital for CyprUs

    I found this one really tricky so think it merits a 3 on the rotor scale, but it will be interesting to see how you get on.

  • GCHQ Puzzle Challenge 15 – Harry’s Hint

    Capital letters

    What is the only possible way to complete this sequence?

    CCR, CR, SV, RBT

    Two hints for this: one, how many items are there in the complete sequence; two have you taken the title seriously?

  • GCHQ Puzzle Challenge 15

    Capital letters

    What is the only possible way to complete this sequence?

    CCR, CR, SV, RBT

    I found this one really tricky so think it merits a 3 on the rotor scale, but it will be interesting to see how you get on.

  • GCHQ Puzzle Solution 14

    One of these things is like the others, one of these things just not belong …

    https://youtu.be/rsRjQDrDnY8
    1. Base sounds the same as (double) bass which can be pronounced differently as the name of a fish!
    2. Bough sounds the same as (taking a) bow which can be pronounced differently as in “violin bow” or “hair bow”
    3. Dessert sounds the same as desert (as in run away) which can be pronounced differently as in Sahara desert.
    4. Doze sounds the same as does (as in the hint) which does have a different pronunciation and meaning doesn’t it!
    5. Pull has no homophones so is the odd one out, BUT ….
    6. Piece sounds the same as peace, but this can only be pronounced one way, so this is the odd one out if you disregard “PULL”. This was the supplementary challenge we set via the forum for those who got 5.
    7. Reed sounds the same as read which can be pronounced to rhyme with “red” instead

    Another from the GCHQ linguistic playbook. If you now your homonyms and synonyms you should have been in good shape, though as with many wordplay games there is an element of cultural bias here, so apologies if your local dialect made this one too tricky!

  • GCHQ Puzzle Challenge 14 – Harry’s Hint

    One of these things is like the others, one of these things just not belong …

    https://youtu.be/rsRjQDrDnY8
    1. Base
    2. Bough
    3. Dessert
    4. Doze
    5. Pull
    6. Piece
    7. Reed

    This doesn’t have anything to do with Sesame Street, but I couldn’t resist. Can you find the odd one out in the list?

  • GCHQ Puzzle Challenge 14

    One of these things is not like the others, one of these things just doesn’t belong …

    https://youtu.be/rsRjQDrDnY8
    1. Base
    2. Bough
    3. Dessert
    4. Doze
    5. Pull
    6. Piece
    7. Reed

    This doesn’t have anything to do with Sesame Street, but I couldn’t resist. Can you find the odd one out in the list?

  • GCHQ Puzzle Solution 13

    You might work out how to get started, but how do you finish?

    Divide the following list into three groups of three:

    1. Be victorious = WIN
    2. Computer network = LAN
    3. Garland of flowers = LEI
    4. Greek Letter = CHI
    5. Companion to “to” = FRO
    6. Mountain pass = COL
    7. Pull = TOW
    8. Little bit (informally) = TAD
    9. University teacher = DON

    Now these are the initial syllables of ancient towns and cities in the UK founded on the sites of roman forts, so they all have chester, cester or caster as their tails:

    1. WINCHESTER
    2. LANCASTER
    3. LEICESTER
    4. CHICHESTER
    5. FROCESTER
    6. COLCHESTER
    7. TOWCESTER
    8. TADCASTER
    9. DONCASTER

    These get grouped as

    1. WINCHESTER
    2. CHICHESTER
    3. COLCHESTER
    1. LEICESTER
    2. FROCESTER
    3. TOWCESTER
    1. LANCASTER
    2. TADCASTER
    3. DONCASTER

    More wordplay from our glorious puzzle masters in Cheltenham.

  • GCHQ Puzzle Challenge 13 – Harry’s Hint

    Don’t know much about history? Don’t know much about geography? Then you might work out how to get started, but could find it hard to finish.

    Divide the following list into three groups of three:

    1. Be victorious
    2. Computer network
    3. Garland of flowers
    4. Greek Letter
    5. Companion to “to”
    6. Mountain pass
    7. Pull
    8. Little bit (informally)
    9. University teacher

    More wordplay from our glorious puzzle masters in Cheltenham.

  • GCHQ Puzzle Challenge 13

    Dictionary attack

    Divide the following list into three groups of three:

    1. Be victorious
    2. Computer network
    3. Garland of flowers
    4. Greek Letter
    5. Companion to “to”
    6. Mountain pass
    7. Pull
    8. Little bit (informally)
    9. University teacher

    More wordplay from our glorious puzzle masters in Cheltenham.

  • GCHQ Puzzle Solution 12

    Look there is a Caesar salad on the (periodic) table!

    2 + 4 = 3

    Second on the table is Helium. He shifted by 4 is Li, so the answer refers to Lithium which is third in the table

    7 + 1 = 8

    The seventh element in the table is Nitrogen with symbol N. Shifting that by 1 gives O which represents Oxygen. Oxygen is eighth in the table

    12 + 1 = 113

    The twelfth element in the periodic table is Magnesium with symbol Mg. Shifting by 1 gives Nh which is the symbol for Nihonium which appears in position 113.

    13 + 2 = 112

    The thirteenth element is Aluminium (Aluminum?) with symbol Al. Shift it by 2 to get Cn, the symbol for Copernicum at position 112.

    20 + 1 = 105

    Twentieth in the table is Calcium with symbol Ca, Shifting by 1 gives Db which is the symbol for Dubnium (surely the coolest and hippest of the elements) at position 105.

    Then what does 10 – 1 equal?

    The tenth element in the table is Neon with symbol Ne. Shifting back by 1 gives Md, the symbol for Mendelevium at position 101!

    The answer is 101 and as of Friday morning no-one had got it, so maybe it should have been a 4 on the rotor scale. This rather cryptic puzzle take symbols from the periodic table and shifts them using a Caesar shift cipher to get others. So, for example, the first one is the symbol for Helium (second element) He, shifted by 4 to give Li, which is Lithium.

    I am not sure I would have got this without a very big hint, so well done if any of you did.