If Kerckhoff's Principle holds, why do we need a cipher at all?
I understand Kerckhoff's principle, in a very practical sense, that the best attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an exhaustive key search, that is, testing every possible key. My question is, if this is the case, then why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
encryption algorithm-design keys
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
add a comment |
I understand Kerckhoff's principle, in a very practical sense, that the best attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an exhaustive key search, that is, testing every possible key. My question is, if this is the case, then why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
encryption algorithm-design keys
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
3
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago
add a comment |
I understand Kerckhoff's principle, in a very practical sense, that the best attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an exhaustive key search, that is, testing every possible key. My question is, if this is the case, then why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
encryption algorithm-design keys
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
I understand Kerckhoff's principle, in a very practical sense, that the best attack that can be performed on a given cryptographic algorithm should be only as practical, if not less practical, than an exhaustive key search, that is, testing every possible key. My question is, if this is the case, then why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
encryption algorithm-design keys
encryption algorithm-design keys
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 1 hour ago
Will Burghard
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 1 hour ago
Will Burghard
161
asked 1 hour ago
Will Burghard
161
161
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
New contributor
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
Will Burghard is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
1
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
3
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago
add a comment |
1
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
3
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago
1
1
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
3
3
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago
add a comment |
1 Answer
1
active
oldest
votes
...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
Designing a cipher is significantly less hassle then using a ridiculously long key.
Designing a cipher only needs to be done once by a competent professional.
Using a ridiculously long key would need to be:
- Done by all parties
- "all parties" includes everyone with a networked electronic device
- Almost all of them are not competent professionals
- Requires a pre-existing secure channel, or more likely a face-to-face meeting
- "secure channel" must not use encryption, otherwise the problem is circular
- Done pairwise for each group of communicating parties
- e.g. You have to go through the key establishment process for every particular site you want to visit
- A web site with 1000 users that each have a 1GB key would need to have access to 1TB of reliable, secure storage just to store the key material (that's a small website)
- Done repeatedly
- You will eventually run out of key material
- Your keys could become compromised
- Updating them in a useful time frame will be next to impossible
- Destroyed securely after use
- Re-using any part of the key will lead to a practical lose of confidentiality
- In a practical scenario (e.g. HTTP requests) known-plaintext attacks apply, which will allow trivial recovery of the key
- Re-using any part of the key will lead to a practical lose of confidentiality
It simply would not work in practice. A proper cipher will.
answered 1 hour ago
Ella Rose♦
15k44178
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
return StackExchange.using("mathjaxEditing", function () {
StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
});
});
}, "mathjax-editing");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "281"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Will Burghard is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcrypto.stackexchange.com%2fquestions%2f66162%2fif-kerckhoffs-principle-holds-why-do-we-need-a-cipher-at-all%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
Designing a cipher is significantly less hassle then using a ridiculously long key.
Designing a cipher only needs to be done once by a competent professional.
Using a ridiculously long key would need to be:
- Done by all parties
- "all parties" includes everyone with a networked electronic device
- Almost all of them are not competent professionals
- Requires a pre-existing secure channel, or more likely a face-to-face meeting
- "secure channel" must not use encryption, otherwise the problem is circular
- Done pairwise for each group of communicating parties
- e.g. You have to go through the key establishment process for every particular site you want to visit
- A web site with 1000 users that each have a 1GB key would need to have access to 1TB of reliable, secure storage just to store the key material (that's a small website)
- Done repeatedly
- You will eventually run out of key material
- Your keys could become compromised
- Updating them in a useful time frame will be next to impossible
- Destroyed securely after use
- Re-using any part of the key will lead to a practical lose of confidentiality
- In a practical scenario (e.g. HTTP requests) known-plaintext attacks apply, which will allow trivial recovery of the key
- Re-using any part of the key will lead to a practical lose of confidentiality
It simply would not work in practice. A proper cipher will.
answered 1 hour ago
Ella Rose♦
15k44178
add a comment |
...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
Designing a cipher is significantly less hassle then using a ridiculously long key.
Designing a cipher only needs to be done once by a competent professional.
Using a ridiculously long key would need to be:
- Done by all parties
- "all parties" includes everyone with a networked electronic device
- Almost all of them are not competent professionals
- Requires a pre-existing secure channel, or more likely a face-to-face meeting
- "secure channel" must not use encryption, otherwise the problem is circular
- Done pairwise for each group of communicating parties
- e.g. You have to go through the key establishment process for every particular site you want to visit
- A web site with 1000 users that each have a 1GB key would need to have access to 1TB of reliable, secure storage just to store the key material (that's a small website)
- Done repeatedly
- You will eventually run out of key material
- Your keys could become compromised
- Updating them in a useful time frame will be next to impossible
- Destroyed securely after use
- Re-using any part of the key will lead to a practical lose of confidentiality
- In a practical scenario (e.g. HTTP requests) known-plaintext attacks apply, which will allow trivial recovery of the key
- Re-using any part of the key will lead to a practical lose of confidentiality
It simply would not work in practice. A proper cipher will.
answered 1 hour ago
Ella Rose♦
15k44178
add a comment |
...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
Designing a cipher is significantly less hassle then using a ridiculously long key.
Designing a cipher only needs to be done once by a competent professional.
Using a ridiculously long key would need to be:
- Done by all parties
- "all parties" includes everyone with a networked electronic device
- Almost all of them are not competent professionals
- Requires a pre-existing secure channel, or more likely a face-to-face meeting
- "secure channel" must not use encryption, otherwise the problem is circular
- Done pairwise for each group of communicating parties
- e.g. You have to go through the key establishment process for every particular site you want to visit
- A web site with 1000 users that each have a 1GB key would need to have access to 1TB of reliable, secure storage just to store the key material (that's a small website)
- Done repeatedly
- You will eventually run out of key material
- Your keys could become compromised
- Updating them in a useful time frame will be next to impossible
- Destroyed securely after use
- Re-using any part of the key will lead to a practical lose of confidentiality
- In a practical scenario (e.g. HTTP requests) known-plaintext attacks apply, which will allow trivial recovery of the key
- Re-using any part of the key will lead to a practical lose of confidentiality
It simply would not work in practice. A proper cipher will.
answered 1 hour ago
Ella Rose♦
15k44178
...why go through the trouble of creating a cipher in the first place? Why not simply use a ridiculously long key, if you're gonna create a cipher that only takes as long as an exhaustive key search anyway?
Designing a cipher is significantly less hassle then using a ridiculously long key.
Designing a cipher only needs to be done once by a competent professional.
Using a ridiculously long key would need to be:
- Done by all parties
- "all parties" includes everyone with a networked electronic device
- Almost all of them are not competent professionals
- Requires a pre-existing secure channel, or more likely a face-to-face meeting
- "secure channel" must not use encryption, otherwise the problem is circular
- Done pairwise for each group of communicating parties
- e.g. You have to go through the key establishment process for every particular site you want to visit
- A web site with 1000 users that each have a 1GB key would need to have access to 1TB of reliable, secure storage just to store the key material (that's a small website)
- Done repeatedly
- You will eventually run out of key material
- Your keys could become compromised
- Updating them in a useful time frame will be next to impossible
- Destroyed securely after use
- Re-using any part of the key will lead to a practical lose of confidentiality
- In a practical scenario (e.g. HTTP requests) known-plaintext attacks apply, which will allow trivial recovery of the key
- Re-using any part of the key will lead to a practical lose of confidentiality
It simply would not work in practice. A proper cipher will.
answered 1 hour ago
Ella Rose♦
15k44178
edited 1 hour ago
answered 1 hour ago
Ella Rose♦
15k44178
answered 1 hour ago
Ella Rose♦
15k44178
answered 1 hour ago
Ella Rose♦
15k44178
15k44178
add a comment |
add a comment |
Will Burghard is a new contributor. Be nice, and check out our Code of Conduct.
Will Burghard is a new contributor. Be nice, and check out our Code of Conduct.
Will Burghard is a new contributor. Be nice, and check out our Code of Conduct.
Will Burghard is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Cryptography Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
Use MathJax to format equations. MathJax reference.
To learn more, see our tips on writing great answers.
Some of your past answers have not been well-received, and you're in danger of being blocked from answering.
Please pay close attention to the following guidance:
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcrypto.stackexchange.com%2fquestions%2f66162%2fif-kerckhoffs-principle-holds-why-do-we-need-a-cipher-at-all%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
1
Related questions: one-time pad: Why is it useless in practice and Is modern encryption needlessly complicated?
– Ella Rose♦
1 hour ago
3
Your question is unclear to me; to convert a plaintext and a key (of whatever length) to a ciphertext, you need an algorithm for transformation. That transformation algorithm is called the cipher. Without a cipher, no encryption, full stop. When you say "why not use a ridiculously long key", how do you intend to encrypt the plaintext?
– marcelm
31 mins ago