Before we dive into sending emails with HTML content and attachments, you’ll learn to send plain-text emails using Python. More than 13.Sending a Plain-Text Email. Use the patcher to apply the translation to your MOTHER 3 ROM. How should we assemble the encryption and the MAC?Inside youll find patcher programs for Windows, Mac, and Linux computers. AES with CBC chaining and PKCS#5 padding) and a standalone MAC (e.g. There are some nifty encryption modes which include a MAC ( EAX, GCM.) but let's assume that we are doing old-style crypto, so we have a standalone encryption method (e.g.Starting a Secure SMTP Connection You’ll learn that a bit later. There’s no fancy stuff like text formatting or hyperlinks.I shall paraphrase it in English, rather than Mathematical notation, as I understand it. Anyway, this paper neatly summarizes all these approaches, and what level of security they do or don't provide. What are the arguments for or against either?I'm assuming you actually know all of this better than I do. Encrypt-then-MAC: Encrypt the cleartext, then compute the MAC on the ciphertext, and append it to the ciphertext? (In that case, we do not forget to include the initialization vector (IV) and the encryption method identifier into the MACed data.)The first two options are often called "MAC-then-encrypt" while the third is "encrypt-then-MAC". Encrypt-and-MAC: Compute the MAC on the cleartext, encrypt the cleartext, and then append the MAC at the end of the ciphertext? (That's what SSH does) And with real-time collaboration, your team can work together from anywhere, whether they’re on Mac, iPad, iPhone, or using a PC.
![]() In other words, we haven't carried any structure from the plaintext into the MAC. The MAC does not provide any information on the plaintext since, assuming the output of the cipher appears random, so does the MAC. If the cipher scheme is malleable we need not be so concerned since the MAC will filter out this invalid ciphertext. EtM ensures you only read valid messages. Assuming the MAC shared secret has not been compromised, we ought to be able to deduce whether a given ciphertext is indeed authentic or has been forged for example, in public-key cryptography anyone can send you messages. The integrity of the plaintext can be verified This opens the door to some chosen-ciphertext attacks on the cipher, as shown in section 4 of Breaking and provably repairing the SSH authenticated encryption scheme: A case study of the Encode-then-Encrypt-and-MAC paradigm. No integrity on the ciphertext again, since the MAC is taken against the plaintext. Here, the MAC cannot provide any information on the plaintext either, since it is encrypted. This is a theoretical point, of course, since practically speaking the MAC secret should provide protection. If the cipher scheme is malleable it may be possible to alter the message to appear valid and have a valid MAC. This occurs if the plaintext messages are repeated, and the MACed data does not include a counter (it does in the SSH 2 protocol, but only as a 32-bit counter, so you should take care to re-key before it overflows).In short, Encrypt-then-MAC is the most ideal scenario. Theoretical, of course, but a less than ideal scenario. May reveal information about the plaintext in the MAC. Of course, any implementation error that can be exploited in the decryption process has been by that point. Note that the padding oracle attacks, which have been applied in the field to ASP.NET, are chosen ciphertext attacks.Ferguson and Schneier, in their book Practical Cryptography, have argued the opposite: that MAC-then-encrypt (or MAC-and-encrypt) is the "natural" order and that encrypt-then-MAC is overly complex. Mostly, it makes it easier to prove the security of the encryption part (because thanks to the MAC, a decryption engine cannot be fed with invalid ciphertexts this yields automatic protection against chosen ciphertext attacks) and also avoids any trouble to confidentiality from the MAC (since the MAC operates on the encrypted text, it cannot reveal anything about the plaintext, regardless of its quality). MAC-then-Encrypt and Encrypt-and-MAC both provide different levels of security, but not the complete set provided by answers the question quite well I just want to add a few details.Encrypt-then-MAC is the mode which is recommended by most researchers. The MAC cannot, also, be used to infer anything about the plaintext. Plain Text Emulator Games Putting Them Together How To Generically ComposeWe show that any secure channels protocol designed to work with any combination of secure encryption (against chosen plaintext attacks) and secure MAC must use the encrypt-then-authenticate method. Encrypt and Authenticate (E&A) used in SSH.It proves that EtA is the secure way to use, and both AtE and E&A are subject to attacks, unless the encryption method is either in CBC mode or it is a stream cipher.The abstract says everything I emphasized important parts by bolding them:We study the question of how to generically compose symmetric encryption and authentication when building “secure channels” for the protection of communications over insecure networks. Authenticate then Encrypt (AtE) used in SSL Encrypt then Authenticate (EtA) used in IPsec To prove their point, Ferguson and Schneier describe an attack over an instance of IPsec in which the encrypt-then-MAC was not done properly.So while encrypt-then-MAC is theoretically better, it is also somewhat harder to get right.Hugo Krawczyk has a paper titled The Order of Encryption and Authentication for Protecting Communications (or: How Secure Is SSL?).It identifies 3 types of combining authentication (MAC) with encryption: The ciphertext is the ENTIRE ciphertext (including IV etc.), and this is what must be MACed. I fully agree with Thomas' first half of the answer, but completely disagree with the second half. Thus, while we show the generic security of SSL to be broken, the current practical implementations of the protocol that use the above modes of encryption are safe.Although there are already many answers here, I wanted to strongly advocate AGAINST MAC-then-encrypt. The same applies to the encrypt-and-authenticate method used in SSH.On the positive side we show that the authenticate-then-encrypt method is secure if the encryption method in use is either CBC mode (with an underlying secure block cipher) or a stream cipher (that xor the data with a random or pseudorandom pad). We show an example of an encryption function that provides (Shannon’s) perfect secrecy but when combined with any MAC function under the authenticate-then-encrypt method yields a totally insecure protocol (for example, finding passwords or credit card numbers transmitted under the protection of such protocol becomes an easy task for an active attacker). You have now just got a full blown padding oracle attack and you are dead. However, if you get an error in the decrypt function, then you return this straight away, as a padding error. By the "straightforward way", what I mean is that you call the "decrypt" function, and afterwards the "mac verify". ![]() Authentication is not designed to obscure the plaintext. Encrypt-and-MAC falls apart for a very simple reason, though: the MAC is not meant to keep the plaintext secret.The MAC is based on the plaintext. The other two, you can debate, but both are at least theoretically sound - one might just practically be better than the other. Business math tutorials for macIf we have a nine digit number plaintext and a one digit checksum, and ship it with the first nine digits encrypted but the checksum not, the checksum is going to help me learn things about the first nine digits of plaintext.
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