First, what is going on here?

We are given:

First, an example:

“oyfjdnisdr rtqwainr acxz mynzbhhx -> Think step by step”

We can see that when “oyfjdnisdr rtqwainr acxz mynzbhhx” is transformed to “Think step by step”

Our task is: Use the example above to decode: “oyekaijzdf aaptcg suaokybhai ouow aqht mynznvaatzacdfoulxxz”

So the first part is to figure out how “oyfjdnisdr rtqwainr acxz mynzbhhx” is decoded into “Think step by step”

Observation 1: The phrase “Think step by step” is 18 letters (excluding spaces) . Let’s count the letters.

Similarly, let’s count the letters in “oyfjdnisdr rtqwainr acxz mynzbhhx”

Original Ciphertext:

oyfjdnisdr rtqwainr acxz mynzbhhx

Plaintext:

Think step by step

First, break down the letters:

Ciphertext letters: o y f j d n i s d r r t q w a i n r a c x z m y n z b h h x

Total letters: Let’s count the letters in the ciphertext.

First word: oyfjdnisdr (10 letters)

Second word: rtqwainr (8 letters)

Third word: acxz (4 letters)

Fourth word: mynzbhhx (8 letters)

Total letters in ciphertext: 10 + 8 + 4 + 8 = 30 letters

Plaintext: Think step by step

First word: Think (5 letters)

Second word: step (4 letters)

Third word: by (2 letters)

Fourth word: step (4 letters)

Total letters in plaintext: 5 + 4 + 2 + 4 = 15 letters

Hmm.

But actually in the problem it says the example:

[Ciphertext] -> Think step by step

So is the decoding process that the ciphertext maps to “Think step by step”?

Our goal is to use the example above to decode:

“oyekaijzdf aaptcg suaokybhai ouow aqht mynznvaatzacdfoulxxz”

First, the cipher seems connected to the plaintext.

Given the time constraints, perhaps the easiest way is to try to see patterns.

Option 1: Try to find mapping from letters to letters.

Do any letters match?

First, let’s write down the ciphertext and plaintext letters on top of each other.

Ciphertext: o y f j d n i s d r r t q w a i n r a c x z m y n z b h h x

Plaintext: T h i n k s t e p b y s t e p

Wait a minute.

I think maybe there is an anagram or substitution cipher here.

Alternatively, I think that we can notice that each group of ciphertext corresponds to a plaintext word.

Check the number of letters.

First ciphertext word: oyfjdnisdr (10 letters)

First plaintext word: Think (5 letters)

Hmm.

Second ciphertext word: rtqwainr (8 letters)

Second plaintext word: step (4 letters)

Third ciphertext word: acxz (4 letters)

Third plaintext word: by (2 letters)

Fourth ciphertext word: mynzbhhx (8 letters)

Fourth plaintext word: step (4 letters)

Interesting.

It seems that the ciphertext words are exactly twice as long as the plaintext words.

(10 vs 5, 8 vs 4, 4 vs 2, 8 vs 4)

Idea: Maybe we need to take every other letter or rebuild the plaintext from the ciphertext accordingly.

Let’s test this theory.

If we take every other letter from the ciphertext words, maybe we’ll get the plaintext.

Let’s try this for the first word:

Ciphertext word: o y f j d n i s d r (10 letters)

Alternate letters:

First letters (positions 1,3,5,7,9): o f d i d

Second letters (positions 2,4,6,8,10): y j n s r

Wait: Let’s try taking every second letter or first letter.

Option 1: Take the odd positions:

Positions: 1 3 5 7 9

Letters: o f d i d

Plaintext word is “Think”, letters are T h i n k

Hmm.

Perhaps we can map letters:

o f d i d –> Think

Not directly

Option 2: Try mapping as per an assigned code: perhaps columns of letters?

Alternatively, perhaps the cipher is more complex.

Alternatively, notice that “oyfjdnisdr” has 10 letters and “Think” has 5 letters.

What if each plaintext letter is being represented by two ciphertext letters?

Similarly for other words.

Suppose that each plaintext letter corresponds to pair of letters in the ciphertext.

Meaning that the first two letters of ciphertext map to the first plaintext letter, and so on.

So for the first word, partition the ciphertext letters into pairs:

oy fj dn is dr

Corresponding to plaintext letters T h i n k

So we can attempt to map:

oy -> T

fj -> h

dn -> i

is -> n

dr -> k

If this is the mapping, perhaps each pair of letters maps to one plaintext letter.

Similarly for other words.

Let’s test this mapping.

Is there a consistent mapping from pairs to letters?

Let’s make a table of pairs and corresponding letters.

First, make the pairs from the first word and their corresponding plaintext letters:

Ciphertext Pairs -> Plaintext Letter

oy -> T

fj -> h

dn -> i

is -> n

dr -> k

Now, what’s the mapping from “oy” to ‘T’?

Is there a way to map ‘oy’ to ‘T’?

Similarly for others.

One possible way is that ‘oy’ represents ‘T’.

But how?

Option 1: Sum of the letters.

Convert letters to numbers (A=1, B=2, …, Z=26)

So let’s try to get to ‘T’ from ‘o’ and ‘y’

o = 15

y = 25

Sum: 15 +25 = 40

But ‘T’ is 20.

Alternatively, perhaps subtract: 25 -15 = 10.

No.

Alternatively, perhaps combine the numbers in some way.

Alternatively, think about their positions in the alphabet.

Alternatively, perhaps the letters are encrypted via a code.

Alternatively, perhaps if we overlay the word ‘Think’ over the cipher pairs ‘oy’, ‘fj’, etc., the cipher is formed by substituting each plaintext letter with two letters.

Alternatively, perhaps consider the ‘original’ letters.

Let’s look at the letters between the word “Think” and “oyfjdnisdr”

Perhaps we can spot that “oyfjdnisdr” is an anagram for “Thinkfiles”?

But that seems unlikely.

Alternatively, think of the pairs.

Suppose we assign numbers to letters: a=1, b=2, …, z=26

Consider the numbers in ‘oy’:

o = 15

y = 25

Add them: 15 + 25 = 40

Now, for ‘T’ we have:

‘T’ is number 20

What if we take the sum of the cipher pair mod 26.

15 +25 = 40

Then 40 mod 26 = 14

14 corresponds to ‘N’

Doesn’t match.

Alternatively, see if the cipher pairs correspond to something else.

Alternatively, perhaps the pair ‘oy’ corresponds to ‘T’ via key.

Alternatively, perhaps it’s as simple as ‘oy’ is ‘T’.

But ‘o’ corresponds to ‘T’, subtracting ‘o’ ASCII code from ‘T’.

Now, let’s think in terms of symmetric letters.

Alternatively, perhaps we can spot that the letters correspond to the first letters of words.

But perhaps an easier way is to look at the word positions.

Alternatively, perhaps we can see that the ciphertext letters are offsets from the plaintext letters.

So let’s try to map the pairs to the plaintext letters.

First pair ‘oy’ and plaintext letter ‘T’

Letter ‘o’ is 15, ‘T’ is 20

Letter ‘o’ + 5 = ‘T’ (15 +5=20)

But ‘y’ is 25, which is 5 letters after ‘T’ (20 +5=25)

Interesting, seems that ‘o’ +5 = ‘T’

Similarly, ‘y’ +1 = ‘Z’, which is not ‘T’.

Alternatively, maybe the average of the two letters corresponds to ‘T’

(15 +25)/2 =20, which is ‘T’

Wait a minute, that seems promising.

First pair: ‘o’ (15) + ‘y’ (25) = 40

40 /2 =20

20 corresponds to ‘T’

So perhaps the average of the letters in the pair corresponds to the plaintext letter.

Let’s check this with the second pair.

Second pair: ‘fj’ corresponding to ‘h’

Letters ‘f’=6, ‘j’=10

Sum: 6+10=16

Average:16/2=8

8 corresponds to ‘h’ (since ‘h’ is 8)

Success!

Third pair: ‘dn’ to ‘i’

‘d’=4, ‘n’=14

Sum:4+14=18

Average:18/2=9

9 corresponds to ‘i’(9=‘i’)

But ‘i’ is 9, so that seems off by 1.

So perhaps we need to think carefully about letters.

Wait, 18/2=9, 9 corresponds to ‘I’

So this works.

Fourth pair: ‘is’ corresponding to ‘n’

‘i’=9, ‘s’=19

Sum:9+19=28

Average:28/2=14

14 corresponds to ‘n’(14=‘N’)

Yes!

Fifth pair: ‘dr’ corresponds to ‘k’

‘d’=4, ‘r’=18

Sum:4+18=22

Average:22/2=11

11 corresponds to ‘k’(11=‘K’)

Perfect!

So our code is: For each pair, sum their numeric values, divide by 2, get the corresponding letter.

Alternatively, the average of the numeric values of the letters corresponds to the plaintext letter.

This seems to be a valid method.

Now let’s test this with the other words.

Second word ciphertext: rtqwainr

Ciphertext pairs:

rt -> s

qw -> ?

ai -> ?

nr -> ?

Corresponding to plaintext letters ‘s’, ‘t’, ‘e’, ‘p’

So let’s take the pairs:

1. ‘rt’ corresponds to ‘s’

r=18, t=20

Sum:38

Average:19

19 corresponds to ‘s’ (19=‘S’)

Good

2. ‘qw’ corresponds to ‘t’

q=17, w=23

Sum:17+23=40

Average:20

20 corresponds to ‘t’ (20=‘T’)

Good

3. ‘ai’ corresponds to ‘e’

a=1, i=9

Sum:10

Average:5

5 corresponds to ‘e’ (5=‘E’)

Good

4. ‘nr’ corresponds to ‘p’

n=14, r=18

Sum:32

Average:16

16 corresponds to ‘p’ (16=‘P’)

Perfect!

Third word: acxz (4 letters)

Plaintext word: ‘by’ (2 letters)

Ciphertext pairs:

a c

x z

Plaintext letters: ‘b’, ‘y’

First pair: ‘a’, ‘c’

a=1, c=3

Sum:4

Average:2

2 corresponds to ‘b’(2=‘B’)

Second pair: ‘x’ and ‘z’

x=24, z=26

Sum:50

Average:25

25 corresponds to ‘y’(25=‘Y’)

Yes!

Fourth word: mynzbhhx (8 letters)

Plaintext word: ‘step’ (4 letters)

Ciphertext pairs:

my

nz

bh

hx

Plaintext letters ‘s’,‘t’,‘e’,‘p’

First pair ‘m’,‘y’

m=13, y=25

Sum:38

Average:19

19 corresponds to ‘s’(19=‘S’)

Second pair: ‘n’,‘z’

n=14, z=26

Sum: 40

Average:20

20=‘t’

Third pair: ‘b’,‘h’

b=2, h=8

Sum:10

Average:5

5=‘e’

Fourth pair: ‘h’,‘x’

h=8, x=24

Sum:32

Average:16

16=‘p’

Got it!

Now, given this, we can decode the given message.

Ciphertext to decode:

“oyekaijzdf aaptcg suaokybhai ouow aqht mynznvaatzacdfoulxxz”

First, we need to divide into words.

Given that the ciphertext in the example had words of length:

-10 letters (5 pairs)
-8 letters (4 pairs)
-4 letters (2 pairs)
-8 letters (4 pairs)

Transported to plaintext words of:

-5 letters
-4 letters
-2 letters
-4 letters

So perhaps in our supplied ciphertext, we need to divide the letters into words accordingly.

Ciphertext: o y e k a i j z d f a a p t c g s u a o k y b h a i o u o w a q h t m y n z n v a a t z a c d f o u l x x z

First, let’s write the letters in order:

1) oyekaijzdf (10 letters) -> word of 5 letters

2) aaptcg (6 letters) -> word of 3 letters

3) suaokybhai (10 letters) -> word of 5 letters

4) ouow (4 letters) -> word of 2 letters

5) aqht (4 letters) -> word of 2 letters

6) mynznvaatzacdfoulxxz (22 letters) -> word of 11 letters

Totals:

So the letters are:

First word: oyekaijzdf (10 letters = 5 pairs)

Second word: aaptcg (6 letters=3 pairs)

Third word: suaokybhai (10 letters=5 pairs)

Fourth word: ouow (4 letters=2 pairs)

Fifth word: aqht (4 letters=2 pairs)

Sixth word: mynznvaatzacdfoulxxz (22 letters=11 pairs)

So we can suppose that the plaintext words have lengths:

1) 5 letters

2) 3 letters

3) 5 letters

4) 2 letters

5) 2 letters

6)11 letters

Now we can proceed to decode.

First word: oyekaijzdf

Divide into pairs:

oy

ek

ai

jz

df

So we can find the plaintext letters by averaging the numeric values of the letters in each pair.

First pair: ‘o’,‘y’

o=15, y=25

Sum=40

Average=20

20=‘T’

Second pair: ‘e’,‘k’

e=5, k=11

Sum=16

Average=8

8=‘H’

Third pair: ‘a’,‘i’

a=1, i=9

Sum=10

Average=5

5=‘E’

Fourth pair: ‘j’,‘z’

j=10, z=26

Sum=36

Average=18

18=‘R’

Fifth pair: ‘d’,‘f’

d=4, f=6

Sum=10

Average=5

5=‘E’

So the first word is ‘T’,‘H’,‘E’,‘R’,‘E’

So ‘THERE’

Second word: aaptcg

Pairs:

aa

pt

cg

First pair: ‘a’,‘a’

a=1, a=1

Sum=2

Average=1

1=‘A’

Second pair: ‘p’,‘t’

p=16, t=20

Sum=36

Average=18

18=‘R’

Third pair: ‘c’,‘g’

c=3, g=7

Sum=10

Average=5

5=‘E’

So second word: ‘A’,‘R’,‘E’

Third word: suaokybhai

Pairs:

su

ao

ky

bh

ai

First pair: s=19, u=21

Sum=40, Average=20

20=‘T’

Second pair: a=1, o=15

Sum=16, Average=8

8=‘H’

Third pair: k=11, y=25

Sum=36, Average=18

18=‘R’

Fourth pair: b=2, h=8

Sum=10, Average=5

5=‘E’

Fifth pair: a=1, i=9

Sum=10, Average=5

5=‘E’

Third word: ‘T’,‘H’,‘R’,‘E’,‘E’

Fourth word: ouow

Pairs: ou, ow

First pair: o=15, u=21

Sum=36, Average=18

18=‘R’

Second pair: o=15, w=23

Sum=38, Average=19

19=‘S’

Fourth word: ‘R’,‘S’

Fifth word: aqht

Pairs: a q, h t

First pair: a=1, q=17

Sum=18, Average=9

9=‘I’

Second pair: h=8, t=20

Sum=28, Average=14

14=‘N’

Fifth word: ‘I’,‘N’

Sixth word: mynznvaatzacdfoulxxz (22 letters: 11 pairs)

Pairs:

m y

n z

n v

a a

t z

a c

d f

o u

l x

x z

Let’s list them properly.

Wait, earlier I missed some letters there.

Let’s re-express the sixth word letters:

m y n z n v a a t z a c d f o u l x x z

Total letters: 22 letters

Pairs:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x x

11. z

Wait, that’s 21 letters.

But in total, we have 22 letters; I think I have a mismatch.

Wait, in the problem the sixth word is:

mynznvaatzacdfoulxxz

Let’s separate the letters:

m y n z n v a a t z a c d f o u l x x z

Total letters: 22 letters

So pairs would be:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x x

11. z

Wait, ‘z’ is only one letter at the end.

So maybe the letters are:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x x

11. z (left alone?)

But then we’re missing a letter.

Alternatively, perhaps the ‘z’ at the end is an extra letter or it’s paired with the previous ‘x’.

Alternatively, perhaps there is a mistake.

Alternatively, perhaps when we reach the last ‘x x z’, we should write:

9. l x

10. x z

Total pairs: 11

So updated pairs:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x z

Now total pairs: 10 pairs. But we are supposed to have 11 letters in the plaintext word.

So perhaps I have miscounted and not considered including ‘f’ or ‘z’.

Wait, is there any chance that the sequence is:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x x

11. z

We have 22 letters.

Perhaps the ‘x x’ and ‘z’ are overlapping.

But we need 11 pairs.

I think for this to work, we need to create 11 pairs from the 22 letters.

So let’s try pairing letters in order, taking two letters at a time.

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x x

11. z ?

But again, last pair only has one letter ‘z’

Alternatively, we might need to adjust the pairs.

Perhaps it’s ‘ou’, ‘lx’, ‘xz’, and there is no extra ‘x’.

Maybe I miswrote.

Wait, let’s write the letters as they come:

m y n z n v a a t z a c d f o u l x x z

Positions:

1 m

2 y

3 n

4 z

5 n

6 v

7 a

8 a

9 t

10 z

11 a

12 c

13 d

14 f

15 o

16 u

17 l

18 x

19 x

20 z

So 20 letters.

Now that makes sense.

Now we can divide into pairs:

Pairs:

1. m y

2. n z

3. n v

4. a a

5. t z

6. a c

7. d f

8. o u

9. l x

10. x z

Total of 10 pairs, which will correspond to 10 letters.

But earlier we thought the word was 11 letters.

But 10 letters may be acceptable.

Maybe we should proceed with the 10 pairs.

First pair: m y

m=13, y=25

Sum=38

Average=19

19=‘S’

Second pair: n z

n=14, z=26

Sum=40

Average=20

20=‘T’

Third pair: n v

n=14, v=22

Sum=36

Average=18

18=‘R’

Fourth pair: a a

a=1, a=1

Sum=2

Average=1

1=‘A’

Fifth pair: t z

t=20, z=26

Sum=46

Average=23

23=‘W’

Sixth pair: a c

a=1, c=3

Sum=4

Average=2

2=‘B’

Seventh pair: d f

d=4, f=6

Sum=10

Average=5

5=‘E’

Eighth pair: o u

o=15, u=21

Sum=36

Average=18

18=‘R’

Ninth pair: l x

l=12, x=24

Sum=36

Average=18

18=‘R’

Tenth pair: x z

x=24, z=26

Sum=50

Average=25

25=‘Y’

So the tenth word is ‘S’, ‘T’, ‘R’, ‘A’, ‘W’, ‘B’, ‘E’, ‘R’, ‘R’, ‘Y’

Wait that’s 10 letters

So the sixth word is ‘STRAWBERRY’, which makes sense.

So putting all these translated letters together:

First word: ‘THERE’

Second word: ‘ARE’

Third word: ‘THREE’

Fourth word: ‘RS’ (? Doesn’t make sense)

Wait, the fourth word, the pairs were:

ou ow

Pairs:

First pair: o u

o=15, u=21

Sum=36, Average=18

18=‘R’

Second pair: o w

o=15, w=23

Sum=38, Average=19

19=‘S’

So we get ‘R’,‘S’

Similarly, fifth word ‘IN’

‘R’, ‘S’ ‘I’,‘N’

So the message so far is

‘THERE ARE THREE RS IN’

And then ‘STRAWBERRY’

Wait, let’s put the words together:

‘THERE ARE THREE Rs IN STRAWBERRY’

I think ‘RS’ is ‘R’s’, meaning ‘Rs’

So the message is:

‘THERE ARE THREE R’S IN STRAWBERRY’

Which is true.

So the decoded message is:

“THERE ARE THREE R’S IN STRAWBERRY”