# Tag Info

94

Why shouldn't I use ECB encryption? The main reason not to use ECB mode encryption is that it's not semantically secure — that is, merely observing ECB-encrypted ciphertext can leak information about the plaintext (even beyond its length, which all encryption schemes accepting arbitrarily long plaintexts will leak to some extent). Specifically, the ...

31

For a real-world example of precisely the same ECB weakness leading to a massive password compromise, see the Adobe password database leak, as memorably illustrated in the xkcd web comic: $\hspace{83px}$ (source: xkcd.com) While there were several issues contributing to the scale of the compromise, one of them was that Adobe, instead of properly hashing the ...

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It illustrates the point that the same plaintext going in to the cipher will result in the same ciphertext. It just happens to be a lot better example than showing someone abc387af de7231ab abc387af abc387af a129867e Now, what does this mean in the real world? If I gave you an email encrypted with AES-128 ECB, could you look at it and figure out the ...

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You should not use ECB mode because it will encrypt identical message blocks (i.e., the amount of data encrypted in each invocation of the block-cipher) to identical ciphertext blocks. This is a problem because it will reveal if the same messages blocks are encrypted multiple times. Wikipedia has a very nice illustration of this problem.

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The Java algorithm string "RSA/ECB/PKCS1Padding", as you already found out, does not implement ECB; it only encrypts/decrypts a single block. The Bouncy Castle cryptographic security provider has a better named algorithm string, "RSA/None/PKCS1Padding", which better indicates that no mode of operation is used. It is likely that "/ECB" was just included to ...

15

It is highly misleading to call how RSA Encryption is used as 'ECB mode'. With ECB mode, we break the plaintext into N bit segments, and send each one through the block cipher separately. The block cipher is deterministic, and so if two plaintext blocks happen to be the same, so will the corresponding ciphertext blocks. Now, with RSA encryption, we take ...

15

Yes, you can do this. In fact, implementing other cipher modes is precisely what ECB mode is good for (and, indeed, just about all it is good for). To implement AES-CTR, simply fill an array of 128-bit blocks with increasing counter values, encrypt it with AES-ECB and XOR the resulting keystream with the plaintext (for encryption) or ciphertext (for ...

15

Assume I have a list of plaintext text and its corresponding ciphertext which was created using a specific key with AES in ECB mode. Can I recover that key? No. This is what is referred to as a known plaintext attack, and secure block ciphers are designed to prevent exactly this kind of attack. This answer on the Mathematics Stack Exchange goes into more ...

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ECB benefits: It's a tiny bit easier to implement. It allows for parallel encryption and decryption (CBC only decryption). A single corrupted cipher block corrupts only one block of plain text(in CBC it is 2) It doesn't need an IV ECB downsides: In almost all cases it is insecure. For comparison, CTR mode allows parallel encryption and decryption and ...

11

ECB leaks if blocks are identical. For uniformly random data identical blocks become likely when you encrypt about $2^{n/2}$ blocks with an $n$ bit block cipher. CBC and CTR mode develop similar weaknesses when they encrypt that much data. => As long as you encrypt reasonable amounts (up to a petabyte or so) of random data with a 128 bit block cipher, like ...

11

Suppose we have a block cipher that takes a 16 byte plaintext and produces a 16 byte ciphertext (that is to say $\mathcal{Enc}: \{0,1\}^{128} \rightarrow \{0, 1\}^{128}$). We use this block cipher to encrypt two blocks worth of unknown data, call them $m1$ and $m2$. Additionally we are allowed to prepend some data to these two blocks, let's call it $m0$ (we ...

11

From a theoretical point as a mode of operation ECB mode has only one advantage over all of the other modes: it doesn't require an IV. That means that the ciphertext doesn't expand if the message is a multiple of the block size or if ciphertext stealing is applied. This can be a benefit e.g. when wrapping another symmetric key (a high entropy message), for ...

10

It is not secure, because an attacker can "mix and match" the output blocks from different authentication tags on different input messages, or repeat output blocks for repeated input blocks. For example, if the attacker knows the tag $F_k(m)$ for a one-block message $m$, then it can forge the correct tag $F_k(m) \mid F_k(m)$ for the two-block message $m \... 10 In the padding oracle attack you have an oracle that only tells you whether a particular chosen ciphertext decrypts to a correctly padded plaintext. That oracle is used to build a last word oracle, which used iteratively can reveal a whole message. The reason it works in CBC mode is that we can make predictable, arbitrary changes to the plaintext of the ... 10 What is the simplest attack is the Brute Force Attack. However, it is infeasible to brute-force even AES-128 bit, AES also supports 192, and 256-bit keys sizes. To break the AES-128 with brute force, you need to execute$2^{128}$AES operations, today's top computers can reach$2^{63}$around one hour. However, reaching$2^{128}$is beyond classical ... 9 The other answer is correct in general. However, if your messages are all exactly one block long (or all one block after padding), ECB is a secure MAC. A PRP looks like a PRF up to half its bit length, i.e. up to$2^{64}$blocks for AES. A secure PRF is a secure MAC of the same size. Thus, AES ECB used on 128-bit messages is a secure MAC as long as you use ... 9 Better is a subjective term. However for the choice between ECB and CBC, the choice should be CBC for almost all situations. Although ECB and CBC are modes of operation of a block cipher, you could also turn this way of thinking around and see the block cipher as a configuration option for the mode of operation. The mode of operation has a big influence on ... 9 Indeed, ECB is such that encrypting twice the same plaintext leads to the same ciphertext. Even worse, encrypting a plaintext containing twice the same plaintext block leads to a ciphertext containing twice the same ciphertext block. Either is a disadvantage because it goes against the ideal of a cipher: depriving the adversary from any knowledge about the ... 9 There is no good way to calculate a strength difference between ECB and CBC. ECB is broken as a generic cipher - it is not indistinguishable under chosen plaintext attack - as repeating blocks will confer information to an attacker. That particular piece of information doesn't let itself be quantified compared to the amount of bits within the key. It's even ... 9 Of course you can implement CTR mode if all you have is ECB. All you have to do is use ECB to encrypt the successive counter values and use the resulting ECB-ciphertext as the CTR keystream to xor with the actual plaintext you want to encrypt. So for example, the first few counter values to encrypt with ECB would be (where$N\$ is a 64 bit nonce / IV which ...

9

Here are some things to keep in mind AES encrypts bytes, not characters. So you have to transform your plaintext into bytes. How are you going to do that? In AES, a block is 128 bits. That is 16 bytes. If your plaintext is only 8 characters long, and each character is encoded as 1 byte, you are short 8 bytes. You can add some padding (a 1 followed by all 0'...

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DES has a block size of 8 bytes. Two blocks therefore come to 16 bytes. It looks like Adbobe were encrypting passwords using two blocks of 3-DES in ECB mode. Because all these passwords are eight bytes long, the second block is empty and is just filled with zeros. The second block gets started at all because of the string-terminating NUL character at the ...

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The modern trend for encryption-only modes is clearly CTR, which has a number of advantages over other modes: no padding is needed (contrary to CBC); the computationally-intensive part can be efficiently performed with the IV (and key) only, before the plaintext or ciphertext is available (contrary to CBC, CFB); the computationally-intensive part can be ...

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The modes you are referencing are specifically modes of operations for block ciphers, and therefore are not directly applicable to hash functions. Block cipher operations take 2 inputs, the key and a block-sized input value, and output a block-sized keyed permutation of the input. Hash functions take a variable length input, and output a fixed length value. ...

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The article mentions that 3-DES was used to encrypt these passwords in ECB mode. DES has a 64-bit/8-byte block. So let's say you use ECB to encrypt a nine byte password. The first 8-bytes are encrypted using ECB. So far so good. But what happens when we come to the ninth byte? Well we're now in a new block but only the first byte is populated with any ...

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The reason why CBC is considered better than ECB has nothing to do with situations involving an attacker with a partial ciphertext; we always assume that any attacker has full access to the ciphertext. Instead, the problem with ECB is that it leaks information. Specifically, if you encrypt two messages which has two blocks of plaintexts in common, then ...

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Your approach seems to have a lot of unneeded complexity and limitations. For example, you must decide the mapping between features and keys in advance. Here are some simpler approaches with more generality: One key per bootloader: Let's call this the client key. Then to send firmware to a particular bootloader you encrypt/authenticate it using that ...

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ECB sucks big time. CBC sucks slightly less, but still a lot. Generally speaking, when you begin to use an encryption system, it is to achieve a number of security-related properties, e.g. confidentiality and integrity of data. An "encryption mode" is a way to turn some elementary cryptographic function (e.g. AES) into something that can process messages of ...

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Classical ciphers operate on letters. If we consider the frequency attack on classical ciphers it considers the frequency of the letters. Modern ciphers, if we consider only block ciphers, operates on blocks - 64, 128, or more bit blocks. Let see how you can perform a frequency attack on modern ciphers to infer some data. Example attack on Databases: Let ...

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Note: I'll disregard the base64 encoding in the following text; the base64 encoding does not change the properties of the generated ciphertext. What you are running into is padding together with ECB mode. This padding can be any static padding. Most common is PKCS#5 padding, but zero padding is also possible. It is not possible to test which padding is used,...

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