Mixing
Does an IV need to be used in AES CTR mode?
Clash Royale CLAN TAG#URR8PPP
up vote
1
down vote
favorite
If I encrypt a message once using AES CTR, will I need an IV? Additionally, if I do use an IV, will I need to send with with the cipher text?
aes stream-cipher initialization-vector ctr
asked Sep 4 at 7:18
Mike
82
add a comment |Â
up vote
1
down vote
favorite
If I encrypt a message once using AES CTR, will I need an IV? Additionally, if I do use an IV, will I need to send with with the cipher text?
aes stream-cipher initialization-vector ctr
asked Sep 4 at 7:18
Mike
82
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
If I encrypt a message once using AES CTR, will I need an IV? Additionally, if I do use an IV, will I need to send with with the cipher text?
aes stream-cipher initialization-vector ctr
asked Sep 4 at 7:18
Mike
82
If I encrypt a message once using AES CTR, will I need an IV? Additionally, if I do use an IV, will I need to send with with the cipher text?
aes stream-cipher initialization-vector ctr
asked Sep 4 at 7:18
Mike
82
asked Sep 4 at 7:18
Mike
82
asked Sep 4 at 7:18
Mike
82
asked Sep 4 at 7:18
Mike
82
82
add a comment |Â
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
2
down vote
accepted
Yes, you need an IV in CTR mode and you do need to send it with the ciphertext, or at least make it possible for the encryption process to know it. Specifically, you need a nonce. The nonce can be anything, as long as it is unique so no key:nonce tuple ever repeats. The nonce is part of the counter. CTR mode operates by encrypting this value and XORing the result with the plaintext. When the next block is to be encrypted, the value is incremented by one and the process repeats.
answered Sep 4 at 7:28
forest
1,976427
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
add a comment |Â
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
2
down vote
accepted
Yes, you need an IV in CTR mode and you do need to send it with the ciphertext, or at least make it possible for the encryption process to know it. Specifically, you need a nonce. The nonce can be anything, as long as it is unique so no key:nonce tuple ever repeats. The nonce is part of the counter. CTR mode operates by encrypting this value and XORing the result with the plaintext. When the next block is to be encrypted, the value is incremented by one and the process repeats.
answered Sep 4 at 7:28
forest
1,976427
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
add a comment |Â
up vote
2
down vote
accepted
Yes, you need an IV in CTR mode and you do need to send it with the ciphertext, or at least make it possible for the encryption process to know it. Specifically, you need a nonce. The nonce can be anything, as long as it is unique so no key:nonce tuple ever repeats. The nonce is part of the counter. CTR mode operates by encrypting this value and XORing the result with the plaintext. When the next block is to be encrypted, the value is incremented by one and the process repeats.
answered Sep 4 at 7:28
forest
1,976427
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
add a comment |Â
up vote
2
down vote
accepted
up vote
2
down vote
accepted
Yes, you need an IV in CTR mode and you do need to send it with the ciphertext, or at least make it possible for the encryption process to know it. Specifically, you need a nonce. The nonce can be anything, as long as it is unique so no key:nonce tuple ever repeats. The nonce is part of the counter. CTR mode operates by encrypting this value and XORing the result with the plaintext. When the next block is to be encrypted, the value is incremented by one and the process repeats.
answered Sep 4 at 7:28
forest
1,976427
Yes, you need an IV in CTR mode and you do need to send it with the ciphertext, or at least make it possible for the encryption process to know it. Specifically, you need a nonce. The nonce can be anything, as long as it is unique so no key:nonce tuple ever repeats. The nonce is part of the counter. CTR mode operates by encrypting this value and XORing the result with the plaintext. When the next block is to be encrypted, the value is incremented by one and the process repeats.
answered Sep 4 at 7:28
forest
1,976427
answered Sep 4 at 7:28
forest
1,976427
answered Sep 4 at 7:28
forest
1,976427
answered Sep 4 at 7:28
forest
1,976427
1,976427
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
add a comment |Â
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
So CTR will not result in producing a same size message correct. It will generate a cipher text of the same size, but the message that is sent will end up being larger since it must include the IV correct?
– Mike
Sep 4 at 7:34
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
@Mike The way you transmit the IV doesn't usually matter. It can be sent with the ciphertext, or with the key. How it is sent is implementation-specific. When it comes to CTR mode itself, it takes plaintext of arbitrary size and outputs ciphertext of the same size, or vice versa. In fact, you can even use an all-zero nonce, as long as you never, ever re-use a single key. All that matters is that the nonce is only used once for each key's keystream.
– forest
Sep 4 at 7:36
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
All modes exception ECB require the receiver to know the IV. If you use a different key for each message then you can use the same IV with most modes (NOT CBC!). Or you can use one key and multiple IVs and transmit the IV each time, but either the key or the IV or both must be made known to the receiver.
– Swashbuckler
Sep 4 at 15:19
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
@Swashbuckler Sure, but each mode has different requirements from their IV.
– forest
Sep 4 at 19:26
add a comment |Â
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
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fcrypto.stackexchange.com%2fquestions%2f62029%2fdoes-an-iv-need-to-be-used-in-aes-ctr-mode%23new-answer', 'question_page');
);
Post as a guest
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
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
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
