Asymmetric cryptography, or public-key cryptography, is the foundation of security protocols that do not require shared secrets.

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Use MDC to provide origin authentication for public key encryption?

Why can't we use an manipultation detection code (MDC) to provide origin authentication when using public-key encryption?
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Security of the shared secret key for a smart meter (Linky) [closed]

Reading the specs of a new electricity smart meter (called Linky in France), I was surprised about the chosen encryption method (128 bits symmetric key AES), based on a single secret key (called CCC ...
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1answer
107 views

Why doesn't my manual RSA key exchange example work?

I'm trying to "manually" compute how the premaster_secret is computed using the RSA key exchange in TLS 1.2, but can't manage to make numbers meet. I am using Scapy SSL to generate a TLS session: I ...
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1answer
106 views

What is the difference between a digital signature and whole message encryption?

I am newbie in information security I am trying to understand the difference between a digital signature and encryption of a message. Lets consider simple example of email message. I understand how ...
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1answer
83 views

How to verify the signature value in a SSL certificate?

According to RFC 3280 a certificate's basic syntax is Sequence := { tbsCertificate signatureAlgorithm signatureValue } In tbsCertificate, SubjectPublicKey is the public key of the ...
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What are the disadvantages of using public key cryptography when encrypting files? [duplicate]

I am wanting to encrypt a file with my public key, my friend told me that this is not a good idea but did not explain why. Can someone explain please.
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1answer
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What does it mean to sign a public key and what's wrong with signing someone else's key?

I just stumbled upon this comic and I'm not sure if I understand what's going on. I googled and I figured that somehow people can sign other people's public keys and then they that person is ...
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70 views

For multiple clients it's better symmetric or assymetric encryption?

I'm a newbie in the encryption world so I'm here for asking which is the best solution between Symmetric and Asymmetric encryption. In our use cases, we have multiple clients that must be ...
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5answers
191 views

Secure application data transmission via SMS channel

There are mobile banking applications that use SMS channel to communicate with their server. Some of them offer both internet and sms channels which the customer gets to choose from. While there's ...
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66 views

how is public key being exchanged in asymmetric cryptography?

I understand that exchanging public key between parties is challenging task in asymmetric cryptography.Can someone help me understand how it is achieved?
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92 views

How are private and public keys different?

While reading about DKIM I saw that the sender's private key is used to encrypt a hash, later decrypted by the recipient using the sender's public key. This is exactly the other way compared to ...
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2answers
104 views

Password based Asymmetric Key generation

I am looking for a password based key derivation scheme that results in an asymmetric key pair. I have worked with PBKDF and its variants but could not come up with any way of generating a key pair. I ...
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1answer
60 views

How to make a good choice between Symmetric and Asymmetric [closed]

Here and there and read a lot of articles and blog posts titled "Difference Between Symmetric Cryptography and Asymmetric Cryptography". But inside of them they are answered "What is Symmetric ...
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What happens if two parties have the same public key? [closed]

What would happen if I get a public key that someone else already has? Isn't the security very weak in that case?
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5answers
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Is it secure to ship public key with license file?

I've implemented a licensing client and server for our web-applications. Currently there is only one way for licensing an app, user should manually upload the license file using specified form and ...
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52 views

stream cipher & e-banking

As I read on internet, I ran into these two question. Yet, I thought about it but still don’t know how to tackle it. May I have your help? (a) During an e-banking transfer the bank uses a stream ...
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3answers
162 views

Public Key Encryption instead of passwords

As an alternative to using passwords, customers could be provided with individual asymmetric-encryption key pairs (i.e. a private key with associated public key), which could be used to validate their ...
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2answers
65 views

Asymmetric Encryption for Multiple Recipients?

Let's assume an arbitrary group of people who hold a key pair and who make their public key online accessible. Let X, A, B and C be arbitrary people from that group. Now X wants to encrypt a message ...
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1answer
55 views

ssl - How is asymetric algorithm used in SSL/TLS?

Okay I have read the questions here on how SSL works, but they all focus on symmetric encryption. But I have configured Apache WebServer to use RSA for SSL using the openSSL tool. Now my question is ...
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4answers
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Why is key exchange necessary at all?

Let's say "Alice" and "Bob" want to communicate with each other over an insecure network. Using Diffie–Hellman key exchange, they can get the same symmetric key at last. However, as I understand, ...
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1answer
44 views

Use asymmetric encryption once to exchange symmetric key

I'm developing a json API that should be able to handle a huge amount of clients. To make this work I need to reduce the overhead as far as possible. One of the ideas I have is to use https only in ...
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3answers
137 views

In message signing, is the digest encrypted with a generated symmetric key or with the sender's private key?

I understand the encryption process uses a generated symmetric key to encrypt a message, and then encrypts the symmetric key with the receiver's public key before it is sent across the wire. This ...
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53 views

Purpose of MAC when encrypting? [duplicate]

Really basic question, but what is the purpose of using a MAC/HMAC when you are encrypting using a symmetric key algorithm? It is my understanding that the purpose of a MAC is to authenticate the ...
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62 views

Curve25519xsalsa20poly1305 key derivation

I'm working on batch-encryption of files, for a small project of mine. The files are stored encrypted on a removable drive, and the keys are stored on a trustful server. For enhanced safety, I'd like ...
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1answer
82 views

In Asymmetric cryptography, is the number of Private Keys limited?

My question is a bit of a leading question, because I assume that the number of Private Keys is a finite number. However, it is possible that the number is such a large number that it would ...
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1answer
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Need asymmetric encryption(not signing) where server encrypts and client decrypts

So I'm trying to build a licensing server, where the licenses of the applications need to be checked when logging in or when the application gets used. But some of those application work offline most ...
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2answers
198 views

Difference between KMS and PKI

While the PKI System deal with digital certificates life cycle and Key Management System (KMS) deal with keys life cycle. What is the the fundamental difference between them? Is it possible to ...
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2answers
209 views

Why can I sign but not encrypt?

-edit- After following a chain of links from this question I see this is similar/duplicate of Why should one not use the same asymmetric key for encryption as they do for signing? but this question ...
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Cloud-based IM protocols / services saving messages encrypted on server which is decryptable only by user? [closed]

I am looking for a cloud-based (i.e. not end-to-end) secure IM protocol or service. The first one comes to my mind is telegram. Here is a quote from telegram's privacy policy: Cloud Chats ...
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1answer
310 views

RSA: same symbols in plaintext give same symbols ciphertext?

I just started studying Information Security, but I just ran this program: http://www.sanfoundry.com/cpp-program-implement-rsa-algorithm/ and faced this strange thing. For small keys (don't try to ...
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1answer
216 views

SQL Server Asymmetric Encryption Keys

I have used SQL Server database with data to be encrypted and I will use symmetric key for encryption and will encrypt it by asymmetric key now comes the question how to give user permission to ...
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2answers
236 views

Can symmetric key cryptography provide identification?

I understand that PKI uses digital certificates to link a public key to an entity, but is there anything similar for symmetric cryptography. If, theoretically, PKI didn't exist, how do you know you ...
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1answer
161 views

Is this symetric or asymetric encryption?

I’m at the beginning of my journey into the world of security. I am reading about the most fundamentals topics and I have encountered something unusual that has thrown me. The Conundrum: I have come ...
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1answer
209 views

How does this encrypted webmails works?

In the last days I was looking on Tutanota, ProtonMail, LavaBoom, and others webmails that promise to respect users privacy. For all those, the one I most liked was Tutanota. I did few tests with ...
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ProtonMail security concerns

This TED talk brought me here. First of all, to those who created ProtonMail: Nice job!!. Regardless of what people say, it's definitely a big step forward from tradition options like Hotmail, Gmail ...
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difference between public key and host key and security of host key

In SSH, what is the difference between host key and public key. Public key I believe that is part of private/public key pair, so, that anything sent by server(encrypted using private) can be ...
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Strength and length of Symmetric vs Asymmetric keys [duplicate]

There are many questions surrounding the differences between symmetric and asymmetric encryption keys. I think I've read them all at this point. But I'm still left wondering: Why does a "secure" ...
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2answers
531 views

Is an >=2048bit key with Asymmetric encryption secure enough to negotiate a Symmetric encryption key?

Let's say that a client app already knows the public key of the server to which it needs to communicate with and the client app needs to connect to the server using a normal non-secured internet ...
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1answer
279 views

“Inverted” asymmetric encryption

I am developing a system to prevent frauds in tickets. What do I need? An algorithm to generate a QR Code that will be shown to my clients in a ticket. An algorithm to validate (offline) the ...
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2answers
874 views

How Securely Store Sensitive Data on Mobile Appliation

i want to develop a mobile bank app (windows phone, android, ios) that interact with bank channel. first time when user opens application the key exchange process begins and at end of this process a ...
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1answer
139 views

All users can write only one can read system

The system I want to implement has the following requirement: All users can insert some sensitive data, but only one, master user, can see it. There is any known, already implemented solution to this ...
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SSL Asymmetric encryption newbie [duplicate]

I am relatively new to the world of cryptography and was wanting to develop a webpage which allows credit card payments. Thus, I looked into the digicert ssl service, hoping that it could do what I ...
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879 views

What's the benefit of hybrid cryptosystem vs asymmetric for small data blocks?

It's a common belief hybrid cryptosystems are better than asymmetric only. Is that allways like that? What's the benefit of using symmetric and asymmetric encryption for small data blocks (< 100 ...
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1answer
106 views

How long can a pkcs#8 passphrase be?

A program is using a private key to read messages. To improve security, besides randomness, I'm trying to create the longest passphrase that makes sense. How long should it be? After which amount of ...
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4answers
886 views

Why the symmetric key is added to the message?

Yesterday in my class we learnt how to send a message from Alice to Bob with the achieved goals of confidentiality, integrity and authenticity. In order to have a better performance we use a hybrid ...
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2answers
408 views

Why does ssh `known_hosts` file need server name?

When I push/pull repos on GitHub over SSH, sometimes there will a message about unidentified server and asks if I want to trust and add it to known_hosts. Apparently this is because GitHub has ...
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1answer
171 views

Is there any asymmetric scheme provides signature with length of 30 bytes?

I want to send short messages to cell phones.Commonly a short message is no longer than 70 bytes. I need 20 bytes or more holding information and the rest bytes are for signature provided by ...
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2answers
177 views

Receiving sensitive data uploaded on a Web server, and remotely accessing it without exposing it to theft

Edit: I mostly used my university's guidelines on how to meet DPA standards and their own. I extrapolated a bit because encryption on a VM hosted by my uni that is already probably encrypted makes ...
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2answers
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Does public key auth in SSH prevent most MITM attacks?

I found this article that claims asymmetric crypto signature of DH-obtained key prevents MITM: http://www.gremwell.com/ssh-mitm-public-key-authentication Key idea: The value of 'signature' is a ...
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Public Key Transfer between two Applications

I have a Service written in c# which uses asymmetric Encryption to Encrypt Data, and a client application which Decrypts the Encrypted data received from the service. How can I do the following ...