Questions tagged [certificates]

A certificate consists of a public key and information about the owner (e. g. the name of a person or server).

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32
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3answers
4k views

Does “Shattered” actually show SHA-1-signed certificates are “unsafe”?

Note: I am not advocating anyone continues using SHA1-signed certificates: they are dead as far as security is concerned and should no longer be used. I'm just trying to clarify my understanding of ...
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4answers
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Recommended skills for a job in cryptology [closed]

First let me apologize if this is an ill posed question. Let me also note that I do not in any way seek a comprehensive answer, simply your thoughts on what makes for a valuable asset to a company ...
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2answers
16k views

Unpredictability of X.509 serial numbers

About X.509 certificates serial numbers the RFC 5280 says: The serial number MUST be a positive integer assigned by the CA to each certificate. It MUST be unique for each certificate issued by a ...
19
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2answers
37k views

Difference between “Signature Algorithm” and “Signature Hash Algorithm” in X.509

What's the difference between the "Signature Algorithm" and the "Signature Hash Algorithm" found in an X.509 certificate? Why does it need a "Signature Hash Algorithm"? Edit: I'm creating the X.509 ...
15
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1answer
628 views

Who issued the first SSL certificate?

When SSL was introduced in ~1996, there was only a few CAs issuing certificates for that specific use and a few sites which actually used SSL. Which Certification Authority issued the first SSL ...
10
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1answer
4k views

Need an introduction to SPKI (or “SPKI for dummies”)

I am familiar with concepts such as the following: PKI and CAs ID based cryptography Certificateless cryptography PGP web of trust more or less anything in basic Crypto that is taught in a college ...
10
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1answer
5k views

Why does the PKCS1 RSA private key structure contain more than just exponent and modulus?

The ASN.1 spec for the PKCS1 RSA private key format is as follows: ...
9
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3answers
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Are there other digital certificate formats than X.509?

Hi I am a little new to security, but in researching digital certificates it seems the only format people describe is X.509. Are there other formats? If so what are they and where can I find ...
9
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2answers
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How does a client verify a server certificate?

As far as I know, when I request a certificate from Verisign (for example), and after they approved that me is me, they create a certificate (for me) which contains the digital signature and public ...
9
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2answers
7k views

How does a certificate authority issue a digital certificate?

I am new to cryptography and I want to know the details of how a Certificate Authority issues a digital certificate. From what I know (please correct me if I'm wrong at any parts of my explanation): ...
8
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2answers
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Why is a CSR signed and which key is used for signing?

I know that a CSR includes a public key from which a signed certificate shall be generated. But why is the CSR istself signed and which key is typically used? For signing I need a private key, so the ...
8
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1answer
6k views

How do other, non-RSA algorithms, compare to the PKCS #1 standard?

Arguably the PKCS suite of standards have a profit-oriented bias as they are promoted by RSA and promote their algorithms over others in the form of RFCs and other means. I'm considering the ...
8
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2answers
270 views

Must root certificates be self signed?

Root certificates are normally self-signed. What is the reason behind that convention? I mean, one must trust the root certificate in a non cryptographic way anyhow.
7
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1answer
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How is OID 2a 86 48 86 f7 0d parsed as 1.2.840.113549?

I saw that an RSA key, created by OpenSSL, contains the following HEX string: 2a 86 48 86 f7 0d 01 01 01 that HEX string gets interpreted as Object ID: 1.2.840.113549.1.1.1 It is obvious 01 01 ...
7
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3answers
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Can we design a public-key infrastructure without certificate authorities?

In a recent essay, Bruce Schneier tasks the engineering community with redesigning and rebuilding the vulnerable parts of the Internet's backbone. We need to figure out how to re-engineer the ...
6
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2answers
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What happens when a root CA has its private key compromised?

What happens when a root CA has its private key compromised? Then all children in the tree are compromised too? And then all certificates are compromised? What needs to happen then? Related: - How ...
6
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2answers
3k views

What exactly is inside a private key?

May sound stupid to many, but I would like to have some pointers on what exactly is contained inside a private key. I have decent understanding of public/private keys/certificates (have created them ...
6
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1answer
27k views

Is PKCS7 a signature format or a certificate format?

I always though PKCS7 was a signature format. However, on the net I find several references to PKCS7 being a certificate format - for example, this talks about PKCS7 certificate: Extract raw ...
6
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2answers
248 views

Is the warning given by chrome warranted?

I went to a payment page on a site recently, and chrome was warning me that the page is possibly not secure, I have a very basic understanding of crypto but not enough to fully understand why this ...
6
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1answer
5k views

What does “G2” mean when used with X509 certficates and certificate authorities?

For example "Google Internet Authority G2"?. I thought it was another way of specifying Class 2 (for organizations, for which proof of identity is required) but then see certificates such as "VeriSign ...
6
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1answer
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Client and server using same SSL certificate - any issues?

I'm working on software where multiple components will communicate with each other using SSL. There would be one central component acting as a server, which would also require the clients to present ...
5
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2answers
245 views

Can S/MIME be still considered secure?

Previoulsy I had asked this question at https://stackoverflow.com/questions/18235983/can-s-mime-be-still-considered-secure but I feel this forum is topic-wise the right place. Recently there has been ...
5
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4answers
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Diffie-Hellman and man-in-the-middle attacks

See here for the man-in-the-middle attack on Diffie-Hellman that I'm concerned about: What is Diffie-Hellman? How do we combat this? I have two questions: Is one solution for both Alice and Bob just ...
5
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2answers
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Diffie-Hellman Key Exchange with Authentication: Man-in-the-Middle query

I have been reading up on MiTM attacks, and the prevention of them using public key certificates. Recently I learnt about Diffie-Hellman Key Exchange with Authentication, and how it uses signed ...
5
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1answer
116 views

Signature verifying against multiple certified public keys?

I'm wondering if and how the current public key certificate infrastructure is guarded against the following scenario: Honest Alice obtains Eve's public key certificate Certe, made by honest CA Carol; ...
4
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3answers
438 views

Deduce modulus N from public exponent and encrypted data

This is an RSA question, given data encrypted with a public key from an unknown RSA certificate of 2048 bit, let $X$ be the encrypted data, $M$ the unencrypted data, $c$ the public exponent and $N$ it'...
4
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2answers
856 views

Why is the signatureAlgorithm field in X.509 certificates redundant?

See the ASN.1 description of an X.509 certificate below: ...
4
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2answers
750 views

X.509 CSR: Why does CA remove signature?

I just read this article on Wikipedia: Certificate Signing Request I'm not a PKI or Crypto expert. As I understand, a CSR (certification request) is always signed by the PKCS#10-Request creator. ...
4
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2answers
3k views

Certificate Authority RSA key expiration?

My understanding about SSL/TLS for HTTPS is that servers send their certificates to browsers and browser attempt to decrypt them using trusted CA public keys that are already presented in their store. ...
4
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4answers
2k views

Signature and Timestamp for Long Term Document Archival Question

I have a PDF document intended for long-term (many years, maybe decades) archival which I would like to digitally sign with my personal certificate to ensure its integrity. As far as I understand, I ...
4
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1answer
2k views

OpenPGP/X.509 bridge: how to verify public key?

I'd like to use OpenPGP authentication over TLS, but lack of implementations made me use a temporary solution: an OpenPGP/X.509 bridge certificate. The approach is very similar to the approach used ...
4
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1answer
1k views

How does certificate-based encryption solve key revocation problem?

How does certificate-based encryption solve key revocation problem? For example, if a user accidentally reveals its secret key or an attacker compromises it, the user may request revocation of its ...
4
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2answers
1k views

How is SSL secure from rogue Certificate Authorities?

There's one thing that I've never quite understood about SSL (which perhaps means I don't understand SSL at all): how is SSL secure from rogue Certificate Authorities? This is probably best ...
4
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1answer
74 views

Why are some websites seemingly immune to self-signed certificate MitM attacks?

I recently did an experiment using MitM to gain account information (username and password) while accessing websites. I used two PCs in the scenario; one as the target, running Internet Explorer, and ...
4
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2answers
714 views

Smart Card - Entropy during on-board public key generation

I know that some (advanced) smart cards or tokens allow generating key pair directly on the device, but I wonder how the card can gather entropy during the process. Any idea ?
4
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1answer
133 views

What security do digital signatures provide (like used when signing PDFs)?

I want to ask you one question about digital signatures as they are (for example) used when digitally signing PDFs. We know that if our document has a digital signature, we can detect if the original ...
3
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2answers
1k views

Certificateless cryptography

While reading "Certificateless Public Key Cryptography" by Author Sattam S. Al-Riyami and Kenneth G. Paterson, they have considered generation of private keys by a Key Generation Center (KGC). If the ...
3
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2answers
169 views

how to let other people respond to emails only decrypt-able with my private key

First of all I have to say it's a homework question but since I have no one to consult with, I ended up here :) Suppose a case in which you are the manager of a company and all employees encrypt ...
3
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1answer
89 views

How can I validate a given Server-Certificate behind a HTTPS-connection?

I know more or less about how TLS works in principle. But how can I be sure, that the certificate behind a server's web site (e.g. tele-banking from my bank) has been issued to my bank and not to ...
3
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3answers
367 views

Does the Shappening mean HTTPS can be broken?

For years we've been warned that SHA-1 is weaker than originally thought and should not be used. This reached its peak with the Shappening and experts from Schneier on down have been warning that we ...
3
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2answers
1k views

TLS Handshake : Server authentication or only Server ‘s Certificate authentication?

I have some difficulty understanding the way in which the Server is really authenticated by Client in TLS handshake (in case of using RSA key exchange). When Client receives Server ‘s Certificate and ...
3
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4answers
131 views

Possible to use an accumulator to “license” or restrict the qty of certificates being used?

Suppose in a future version of x509 PKI, it is possible to limit the quantity of certificates being used, what would that look like? Here is a concept that won't work in the real world, but ...
3
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2answers
6k views

How do digital certificates work, and why is it not possible to reverse engineer one from a signed file?

Digital certificates are used quite commonly these days, for signing files. They are used by various operating systems to ensure reliability and security. For example, Android requires that each of ...
3
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1answer
46 views

What is the RFC order of peer certificate verification, trust chain or expiry first?

If a certificate received from a peer: Is expired, has a valid signature, but from an untrusted root CA What error should be thrown? Untrusted certificate or expired certificate? I can't seem to ...
3
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1answer
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Extra attributes in a certificate signing request

When creating a certificate signing request, there is a part where openssl says "Please enter the following extra attributes to be sent with your certificate request". One of these is a challenge ...
3
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1answer
85 views

How is the root certificate transmitted to pc?

i understand that the purpose of root certificates and CA's is to ensure that the communication parties are who they say they are. But how is the root certificate acquired? Is it not possible that ...
3
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1answer
117 views

X509 certificates: Two Algorithm Identifiers?

I'm wondering why there are two Algorithm Identifiers in a X509 certificate. One is in the "to be signed" part and the other one is at the end right before the actual signature. Are they used for the ...
3
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1answer
4k views

x509 Certificate Signature

I've got a question about the signature of a CA. As I understand, the CA takes the public key of the client and signs it with his own private key by using "md5WithRSAEncryption" (like explained here: ...
3
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0answers
617 views

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? [closed]

Are any Certificate Authorities using 4096 bit keys for their intermediate and root certificates? I know you can, of course, use a 4096 bit key for your server certificate, but I usually see 2048 bit ...
3
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1answer
43 views

Shortest Path for Certificate Network

I was reading an example from my textbook about verifying a certificate from a client using a certificate network. The example in the book is as follows: A issues a certificate to B. A issues ...