Lesson 3: Explain Cryptographic Solutions Flashcards
Define ‘Cryptography’
The science and practice of encoding or decoding data to make it unintelligible to unauthorized parties.
Define ‘security through obscurity’
Keeping something a secret by hiding it.
Define ‘Plaintext/Cleartext’
Unencrypted data.
Define ‘Ciphertext’
Encrypted data that can’t be read without the cipher key.
Define an ‘Algorithm’
Process that encrypts and decrypts data.
Define ‘Cryptanalysis’
The science/practice of breaking ciphers and cryptographic systems.
Define an ‘Encryption’ algorithm/cipher
Process that encodes data so that it can be stored or transmitted securely and then decrypted only by its owner or its intended recipient.
Define a ‘key’ in cryptography
Specific piece of data that is used in an algorithm to perform encryption and decryption.
What are the two types of encryption algorithms?
- Symmetric
- Asymmetric
Define a ‘substitution’ cipher/algorithm
Replacing characters or blocks in the plaintext with different text or ciphertext.
Define a ‘Transposition’ cihper/algorithm
The units of data stay the same, but their order is changed depending on the mechanism.
Define ‘Symmetric Encryption’
Shared-key encryption; Two-way encryption process in which encryption and decryption are both performed by the same key.
What is the benefit of symmetric encryption?
Used for bulk encryption of large amounts of data due to its speed; Very fast
What is the security risk in symmetric encryption?
The transmission/receipt of the shared-key; Security is broken if the key is intercepted along with the cipher text.
Define ‘key length’
Size of a cryptographic key in bits; Longer keys generally offer better security and are harder to crack with brute force.
What is the downside to using larger encryption keys?
The computer must use more resoruces to perform encryption and decryption.
Define ‘Asymmetric Encryption’
One-way encryption; Cipher that uses public and private keys mathematically linked by RSA or ECC algorithms;
What is the difference between asymmetric encryption and symmetric encryption?
An asymmetric key cannot reverse the operation it performs; The public key cannot decrypt what it has encrypted and vise versa.
What is the function of the public key in asymmetric encryption?
Key is freely distributed and can be used to perform reverse encryption or decryption operation of the linked private key in the pair.
What is the function of the private key in asymmetric encryption?
Uniquely associated with the owner and is not made public; Used to encrypt data that can be decrypted by the linked public key or vice versa.
What is a downfall of asymmetric encryption?
Involves substantial computing overhead compared to symmetric encryption and is inefficient for large amounts of data.
How can the overhead from asymmetric encryption be mitigated with large amounts of data?
Asymmetric encryption can be used to encrypt a symmetric key that was used to encrypt data before transmitting the data.
Define ‘cryptographic hashing’ algorithms
One-way encryption that produces a fixed-length string of bits from a plaintext input.
What does a hashing algorithm produce?
The output is a ‘hash’ or ‘message digest’
What is the typical function/purpose of hashing algorithms?
To prove integrity; Ensure that data has not been manipulated in transmission/receipt/storage and for authentication.
What are the two popular hashing algorithms?
- Secure Hash Algorithm (SHA)
- Message Digest Algorithm #5 (MD5)
Define ‘Secure Hash Algorithm (SHA)’
Replacement for message digest algorithm (MDA); Considered strongest - most popular is SHA256 producing a 256-bit digest.
Define ‘Message Digest Algorithm #5 (MD5)’
Considered not as safe as SHA256; Produces a 128-bit digest.
Define a ‘cryptographic primitive’
A single hash function, symmetric cipher, or asymmetric cipher.
Define a ‘complete cryptographic system/product’
The use of multiple cryptographic primitives within a cipher suite.
What two forms of cryptography combine to create a digital signature?
Combines Asymmetric encryption for confidentiality to authenticating the sender with hashing to provide integrity.
What is ‘Public Key Infrastructure (PKI)’
Framework that establishes trust in the use of public key cryptography to sign and encrypt messages via digital certificates.
What is the purpose of Public Key Infrastructure (PKI)?
To prove the owners of public keys are who they say they are.
Define a ‘Digital Certificate’
A public assertion of identity, authenticated by a certificate authority (CA) that contains a subjects public key.
Define a ‘certificate authority (CA)’
A server that guarantees subject identities by issuing signed digital certificate wrappers for their public keys.
What is a 3rd party certificate authority (CA)?
A public CA that issues certificates for multiple domains; Widely trusted as a root trust by operating systems and browsers.
What purpose of a 3rd party public CA?
- Provide a range of cert services.
- Ensure the validity of certs and the identity of those applying for them.
- Manage the repositories that store and administer certs.
- Key and cert lifecycle management (revoking invalid certs).
How does a subject generate a certificate from a public 3rd party root CA?
- Register to the CA to prove identity
- Generate a cert signing request (CSR) from a webserver containing the public key and submit the CSR to CA for validation
- CA generates a signed cert with the public key and sends to subject.
- Publishing of cert in webservice manager (IIS/Apache/other)
Define a ‘digitally signed certificate’
Proof that a cert was validly issued to a subject (user/host) by a public 3rd party root CA.
When going to a URL, how does the client verify identity?
- Client checks web server’s certificate and validates that it is signed by a trusted CA.
What is packaged in a digitally signed cert?
Information identifying the subject and the public key authenticating the connection presented in X.509 format, and digital signature from the issuing CA.
Define a ‘root certificate/trusted root’
Pre-installed self-signed cert and public key from a CA.
What is the purpose/function of a root certificate?
Issues signed certificates to intermediate CAs; Sign other certificates issued by the CA;
How do clients trust a public 3rd party root CA?
- CA generates a root certificate, signs it with private key, and publishes it with the public key.
- Client obtains CA’s certificate and adds it to a store of trusted root certificates.
What is the outcome of installing a CA’s root certificate?
Host will automatically trust any certificates signed by that CA.
Define a ‘Single CA’ model
Single root CA issues certificates directly to users and computers; Often used on private networks.
What is the shortcoming of the single CA model?
Single CA server is exposed; If it is compromised the whole PKI collapses.
Define the ‘3rd party CA model’
Hierarchical model where the root CA issues certs to one or more intermediate CAs; The intermediate CAs issue certs to subjects (end entities).
Define ‘certificate chaining’ or ‘chain of trust’
Method of validating a certificate by tracing each CA that signs the certificate, up through the hierarchy to the root CA.
Define a ‘Self-signed Certificate’
A digital certificate that has been signed by the entity that issued it (any machine, webserver or code), rather than by a CA.
What is the process to register with a CA?
End users create an account with the CA and become authorized to request certificates.
What is the contents of a ‘certificate signing request (CSR)’?
A Base64 ASCII file containing the information that the subject wants to use in the certificate, including its public key.
Define a ‘common name (CN)’
X.500 certificate identifier expressing a host or username; The subject identifier for a digital certificate.
Define a ‘subject alternative name (SAN)’
X.500 certificate identifier allowing a host to be represented by multiple host names/subdomains.
What takes precedence in a certificate, a subject alternative name (SAN) or common name (CN)?
If a certificate is configured with a SAN, the browser should validate that and ignore the CN value.
Define a ‘wildcard certificate’
A digital certificate that will match multiple subdomains of a parent domain using a ‘’ as the subdomain before the parent domain (.comptia.org)
What are the two types of invalid certificates?
- Revoked - no longer valid and can’t be unrevoked
- Suspended and can be reenabled
Define a ‘certificate revocation list (CRL)’
A list maintained by a CA of all revoked and suspended certificates.
What is the purpose of a certificate revocation list (CRL)?
To inform users whether a certificate is valid, revoked, or suspended.
Where can a certificate revocation list (CRL) be found for browsers to check validity of certs?
Each certificate should contain information for the browser on how to check the CRL.
What are the 4 attributes of a certificate revocation list (CRL)?
- Publish Period
- Distribution Points
- Validity Period
- Signature
Define the ‘Publish Period’ attribute of a certificate revocation list (CRL)
Date and time at which the CRL is published. Most CAs are set up to publish the CRL automatically.
Define the ‘Distribution Point(s)’ attribute of a certificate revocation list (CRL)
Location(s) to which the CRL is published.
Define the ‘Validity Period’ attribute of a certificate revocation list (CRL)
Period during which the CRL is considered authoritative. This is usually a bit longer than the publish period
Define the ‘Signature’ attribute of a certificate revocation list (CRL)
CRL is signed by the CA to verify its authenticity.
Define an ‘Online Certificate Status Protocol (OCSP)’ server
Allows clients to request the status of a digital certificate by querying the certificate database directly instead of relying on a CRL.