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How safe is a book cipher? How would you break it?
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This might not be a very specific question, but I was wondering this morning.
If one were to encode a message by making a string out of an entire book and writing the message by searching for a random occurrence in the "book-string" of each letter in the message and replacing it with the string index of the letter. Additionally you could make sure no number appears twice in the message as there is normally more than one occurrence of each letter in a book. This way no "letter" in the encrypted message would repeat.
How safe is this, assuming you passed on the key safely, and how would you go about breaking it?
Thanks in advance :D
encryption
asked 2 hours ago
Ciaran Hagen
83
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Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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show 3 more comments
up vote
1
down vote
favorite
This might not be a very specific question, but I was wondering this morning.
If one were to encode a message by making a string out of an entire book and writing the message by searching for a random occurrence in the "book-string" of each letter in the message and replacing it with the string index of the letter. Additionally you could make sure no number appears twice in the message as there is normally more than one occurrence of each letter in a book. This way no "letter" in the encrypted message would repeat.
How safe is this, assuming you passed on the key safely, and how would you go about breaking it?
Thanks in advance :D
encryption
asked 2 hours ago
Ciaran Hagen
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
1
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago
 |Â
show 3 more comments
up vote
1
down vote
favorite
up vote
1
down vote
favorite
This might not be a very specific question, but I was wondering this morning.
If one were to encode a message by making a string out of an entire book and writing the message by searching for a random occurrence in the "book-string" of each letter in the message and replacing it with the string index of the letter. Additionally you could make sure no number appears twice in the message as there is normally more than one occurrence of each letter in a book. This way no "letter" in the encrypted message would repeat.
How safe is this, assuming you passed on the key safely, and how would you go about breaking it?
Thanks in advance :D
encryption
asked 2 hours ago
Ciaran Hagen
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
This might not be a very specific question, but I was wondering this morning.
If one were to encode a message by making a string out of an entire book and writing the message by searching for a random occurrence in the "book-string" of each letter in the message and replacing it with the string index of the letter. Additionally you could make sure no number appears twice in the message as there is normally more than one occurrence of each letter in a book. This way no "letter" in the encrypted message would repeat.
How safe is this, assuming you passed on the key safely, and how would you go about breaking it?
Thanks in advance :D
encryption
encryption
asked 2 hours ago
Ciaran Hagen
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
Ciaran Hagen
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
Ciaran Hagen
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 hours ago
Ciaran Hagen
83
asked 2 hours ago
Ciaran Hagen
83
83
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Ciaran Hagen is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
1
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago
 |Â
show 3 more comments
So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
1
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago
So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
1
1
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago
 |Â
show 3 more comments
2 Answers
2
active
oldest
votes
up vote
2
down vote
accepted
This isn't very secure. Generally, partial knowledge of the plaintext should not lead to leakage of other parts of the plaintext. In your book cipher it clearly does.
Say we guess the first part of the message. Then we can try and see which books would be correct for the given ciphertext. After the book (the key) is found we can then decrypt the rest of the message.
answered 55 mins ago
Maarten Bodewes
48.3k568179
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
add a comment |Â
up vote
1
down vote
What you are proposing is just a homophonic substitution cipher and it is highly insecure for modern standards.
It doesn't satisfy common security definitions, such as "security against chosen plaintext attack". It is not semantic secure in the sense that an attacker can easily construct two different messages whose corresponding ciphertexts are guessable.
For instance, the letter Z is not frequently used, so how many times does Z appear in a usual book?
Thus, the message
"When I got there, he was like ZZZZZZZZZZZZZZZZZZZZZZZZZZ sleeping hard"
is much more likely to have repeated digits in its ciphertext than
"When I got there, he was reading an old book about computer science and art."
But even if you stick with weaker security definitions, like just requiring that someone having access to "some" ciphertexts is not able to recover the plaintext, it is still not very secure, because one can use all sort of frequency analysis against it. For instance, which are the most common 3-letter words? Maybe "the", "one", "are"... So we could try to replace them in the ciphertexts and see if it works. If some of them works, then we have already discovered some information about the plaintext and the key...
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
add a comment |Â
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
This isn't very secure. Generally, partial knowledge of the plaintext should not lead to leakage of other parts of the plaintext. In your book cipher it clearly does.
Say we guess the first part of the message. Then we can try and see which books would be correct for the given ciphertext. After the book (the key) is found we can then decrypt the rest of the message.
answered 55 mins ago
Maarten Bodewes
48.3k568179
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
add a comment |Â
up vote
2
down vote
accepted
This isn't very secure. Generally, partial knowledge of the plaintext should not lead to leakage of other parts of the plaintext. In your book cipher it clearly does.
Say we guess the first part of the message. Then we can try and see which books would be correct for the given ciphertext. After the book (the key) is found we can then decrypt the rest of the message.
answered 55 mins ago
Maarten Bodewes
48.3k568179
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
This isn't very secure. Generally, partial knowledge of the plaintext should not lead to leakage of other parts of the plaintext. In your book cipher it clearly does.
Say we guess the first part of the message. Then we can try and see which books would be correct for the given ciphertext. After the book (the key) is found we can then decrypt the rest of the message.
answered 55 mins ago
Maarten Bodewes
48.3k568179
This isn't very secure. Generally, partial knowledge of the plaintext should not lead to leakage of other parts of the plaintext. In your book cipher it clearly does.
Say we guess the first part of the message. Then we can try and see which books would be correct for the given ciphertext. After the book (the key) is found we can then decrypt the rest of the message.
answered 55 mins ago
Maarten Bodewes
48.3k568179
answered 55 mins ago
Maarten Bodewes
48.3k568179
answered 55 mins ago
Maarten Bodewes
48.3k568179
answered 55 mins ago
Maarten Bodewes
48.3k568179
48.3k568179
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
add a comment |Â
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
You're right... simple guessing could pretty quickly limit the number of possible books! Thanks.
– Ciaran Hagen
53 mins ago
add a comment |Â
up vote
1
down vote
What you are proposing is just a homophonic substitution cipher and it is highly insecure for modern standards.
It doesn't satisfy common security definitions, such as "security against chosen plaintext attack". It is not semantic secure in the sense that an attacker can easily construct two different messages whose corresponding ciphertexts are guessable.
For instance, the letter Z is not frequently used, so how many times does Z appear in a usual book?
Thus, the message
"When I got there, he was like ZZZZZZZZZZZZZZZZZZZZZZZZZZ sleeping hard"
is much more likely to have repeated digits in its ciphertext than
"When I got there, he was reading an old book about computer science and art."
But even if you stick with weaker security definitions, like just requiring that someone having access to "some" ciphertexts is not able to recover the plaintext, it is still not very secure, because one can use all sort of frequency analysis against it. For instance, which are the most common 3-letter words? Maybe "the", "one", "are"... So we could try to replace them in the ciphertexts and see if it works. If some of them works, then we have already discovered some information about the plaintext and the key...
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
add a comment |Â
up vote
1
down vote
What you are proposing is just a homophonic substitution cipher and it is highly insecure for modern standards.
It doesn't satisfy common security definitions, such as "security against chosen plaintext attack". It is not semantic secure in the sense that an attacker can easily construct two different messages whose corresponding ciphertexts are guessable.
For instance, the letter Z is not frequently used, so how many times does Z appear in a usual book?
Thus, the message
"When I got there, he was like ZZZZZZZZZZZZZZZZZZZZZZZZZZ sleeping hard"
is much more likely to have repeated digits in its ciphertext than
"When I got there, he was reading an old book about computer science and art."
But even if you stick with weaker security definitions, like just requiring that someone having access to "some" ciphertexts is not able to recover the plaintext, it is still not very secure, because one can use all sort of frequency analysis against it. For instance, which are the most common 3-letter words? Maybe "the", "one", "are"... So we could try to replace them in the ciphertexts and see if it works. If some of them works, then we have already discovered some information about the plaintext and the key...
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
add a comment |Â
up vote
1
down vote
up vote
1
down vote
What you are proposing is just a homophonic substitution cipher and it is highly insecure for modern standards.
It doesn't satisfy common security definitions, such as "security against chosen plaintext attack". It is not semantic secure in the sense that an attacker can easily construct two different messages whose corresponding ciphertexts are guessable.
For instance, the letter Z is not frequently used, so how many times does Z appear in a usual book?
Thus, the message
"When I got there, he was like ZZZZZZZZZZZZZZZZZZZZZZZZZZ sleeping hard"
is much more likely to have repeated digits in its ciphertext than
"When I got there, he was reading an old book about computer science and art."
But even if you stick with weaker security definitions, like just requiring that someone having access to "some" ciphertexts is not able to recover the plaintext, it is still not very secure, because one can use all sort of frequency analysis against it. For instance, which are the most common 3-letter words? Maybe "the", "one", "are"... So we could try to replace them in the ciphertexts and see if it works. If some of them works, then we have already discovered some information about the plaintext and the key...
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
What you are proposing is just a homophonic substitution cipher and it is highly insecure for modern standards.
It doesn't satisfy common security definitions, such as "security against chosen plaintext attack". It is not semantic secure in the sense that an attacker can easily construct two different messages whose corresponding ciphertexts are guessable.
For instance, the letter Z is not frequently used, so how many times does Z appear in a usual book?
Thus, the message
"When I got there, he was like ZZZZZZZZZZZZZZZZZZZZZZZZZZ sleeping hard"
is much more likely to have repeated digits in its ciphertext than
"When I got there, he was reading an old book about computer science and art."
But even if you stick with weaker security definitions, like just requiring that someone having access to "some" ciphertexts is not able to recover the plaintext, it is still not very secure, because one can use all sort of frequency analysis against it. For instance, which are the most common 3-letter words? Maybe "the", "one", "are"... So we could try to replace them in the ciphertexts and see if it works. If some of them works, then we have already discovered some information about the plaintext and the key...
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
edited 20 mins ago
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
answered 35 mins ago
Hilder Vitor Lima Pereira
3,794828
3,794828
add a comment |Â
add a comment |Â
Ciaran Hagen is a new contributor. Be nice, and check out our Code of Conduct.
Ciaran Hagen is a new contributor. Be nice, and check out our Code of Conduct.
Ciaran Hagen is a new contributor. Be nice, and check out our Code of Conduct.
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So, is your key the book?
– Hilder Vitor Lima Pereira
1 hour ago
Yes it is... You would have the same version and everything of vourse...
– Ciaran Hagen
1 hour ago
1
Could you give an example on how this encryption would look like?
– Aleksander Rassasse
1 hour ago
For example assume your book-string is "abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz"
– Ciaran Hagen
1 hour ago
The more you use this book the more it will reveal itself. A brute-force attack, construct all the books and see what i can get.
– kelalaka
1 hour ago