You may use a desk like this:

   ABCDEFGHIJKLMNOPQRSTUVWXYZ

 A abcdefghijklmnopqrstuvwxyz
 B bcdefghijklmnopqrstuvwxyza
 C cdefghijklmnopqrstuvwxyzab
 D defghijklmnopqrstuvwxyzabc
 E efghijklmnopqrstuvwxyzabcd
 F fghijklmnopqrstuvwxyzabcde
 G ghijklmnopqrstuvwxyzabcdef
 H hijklmnopqrstuvwxyzabcdefg
 I ijklmnopqrstuvwxyzabcdefgh
 J jklmnopqrstuvwxyzabcdefghi
 Ok klmnopqrstuvwxyzabcdefghij
 L lmnopqrstuvwxyzabcdefghijk
 M mnopqrstuvwxyzabcdefghijkl
 N nopqrstuvwxyzabcdefghijklm
 O opqrstuvwxyzabcdefghijklmn
 P pqrstuvwxyzabcdefghijklmno
 Q qrstuvwxyzabcdefghijklmnop
 R rstuvwxyzabcdefghijklmnopq
 S stuvwxyzabcdefghijklmnopqr
 T tuvwxyzabcdefghijklmnopqrs
 U uvwxyzabcdefghijklmnopqrst
 V vwxyzabcdefghijklmnopqrstu
 W wxyzabcdefghijklmnopqrstuv
 X xyzabcdefghijklmnopqrstuvw
 Y yzabcdefghijklmnopqrstuvwx
 Z zabcdefghijklmnopqrstuvwxy

The primary two letters of the reply can then be used to discover a row and column, leading to a code letter to confirm the reply. The identical can then be completed or the third and fourth letters of the reply. The query may have the verification code nq, and in the event you thought the reply was NAME, you’ll lookup NxA to offer n, MxE to offer q and know that you simply have been in all probability right.

Each query ought to after all have the identical variety of verification letters so you do not get a clue to the size of the reply, so utilizing simply 2 verification letters to match the primary 4 letters of the reply appears cheap. If there are shorter solutions, it’s possible you’ll want so as to add an additional rule like padding it with x’s to make it 4 letters.

Observe that the desk is symmetric, so it would not matter which letter you employ for the column and which for the row. Nevertheless, a sensible child may have a look at the desk, see the sample and use it to get a clue in regards to the reply, so it might in all probability be higher to randomise the desk like this:

   ABCDEFGHIJKLMNOPQRSTUVWXYZ

 A wgieodlrqbhufxzaspymtvjcnk
 B gqsoynvbalrephjkcziwdftmxu
 C isuqapxdcntgrjlmebkyfhvozw
 D eoqmwltzyjpcnfhiaxgubdrkvs
 E oyawgvdjitzmxprskhqelnbufc
 F dnplvksyxiobmeghzwftacqjur
 G lvxtdsagfqwjumophenbikyrcz
 H rbdzjygmlwcpasuvnkthoqexif
 I qacyixflkvbozrtumjsgnpdwhe
 J blnjtiqwvgmzkcefxudryaohsp
 Ok hrtpzowcbmsfqikldajxegunyv
 L uegcmbjpozfsdvxyqnwkrthali
 M fprnxmuazkqdogijbyhvceslwt
 N xhjfpemsrcivgyabtqznuwkdol
 O zjlhrgoutekxiacdvsbpwymfqn
 P akmishpvuflyjbdewtcqxzngro
 Q sceakzhnmxdqbtvwoluiprfyjg
 R pzbxhwekjuanyqstlirfmocvgd
 S yikgqfntsdjwhzbcuraovxlepm
 T mwyuetbhgrxkvnpqifocjlzsda
 U tdfblaionyercuwxpmvjqsgzkh
 V vfhdnckqpagtewyzroxlsuibmj
 W jtvrbqyedouhskmnfclzgiwpax
 X cmokujrxwhnaldfgyveszbpitq
 Y nxzvfucihsylwoqrjgpdkmateb
 Z kuwscrzfepvitlnogdmahjxqby

I generated this desk by placing the 26 letters of the alphabet in a random order, placing these on the prime and alongside the left of the unique desk, after which sorting the rows and columns in alphabetical order. This desk continues to be symmetric, however a lot more durable to get a sample from.