SSL certificate (PEM/CRT) information analysis/validity decoder | ZeroTools

X.509 v3, the electronic certificate standard that supports public key infrastructure, has an extremely strict data structure defined in RFC 5280.

The decoding engine starts by detecting a PEM format header, which is a Base64 encoded text format, that is, a string surrounded by hyphens, and converting it into binary data stored internally.

It then traverses at the binary level a hierarchical data structure organized according to ASN.1's DER encoding rules. DER uses a TLV structure in which each data element is represented by three elements: tag, length, and value.

During the decoding process, these byte sequences are read sequentially from the beginning, and the three main blocks that make up the certificate, the body data, signature algorithm identifier, and signature value, are precisely separated and expanded in memory.

This converts the complex nested ASN.1 structure into a flat data model that can be handled within the program, allowing subsequent detailed attribute analysis.

Furthermore, the decoding engine constantly monitors for parsing inconsistencies up to the end of the data stream, and has a safety mechanism that immediately stops parsing if it detects an abnormal value in the length field or an unspecified tag number, and also plays a role in preventing system failures such as buffer overruns caused by reading certificate files with incorrect structures.

A very important role in the analysis of the certificate body is the deciphering of the distinguished name, which is the identification information of the subject and the issuer.

These are stored as a sequence of relative distinguished names, where each attribute such as country name, organization name, common name, etc.

is associated with a unique object identifier.

The parsing model interprets these object identifiers as directory strings and converts them to human-readable strings using encoding rules such as UTF8String and PrintableString.

At the same time, by extracting the serial number, which is a unique identifier assigned by the certification authority, and processing it as a multiple-length integer, even huge numbers can be accurately represented.

Validity parsing, which is essential for determining the validity of a certificate, reads the start and end date and time fields expressed in Coordinated Universal Time and converts them to date and time objects based on the system's local time zone.

This date and time parsing process supports both formats expressed in two-digit years and formats expressed in four-digit years, and by incorporating flexible interpretation logic compatible with the 2000-year problem, it provides the basis for accurate validity verification on a second-by-second basis for the entire system.

Parsing the extensions added in X.509 v3 is an essential part of modern SSL and TLS certificate operations. In particular, subject alternative names are used to protect multiple domain names or IP addresses with a single certificate, and the parsing process identifies tagged elements such as dNSName and iPAddress and extracts them as a list of strings according to their respective formats.

It is also important to analyze key usage and extended key usage, which limit the permitted uses of public keys.The former involves expanding fragments such as digital signatures and key encryption stored as bit strings into individual truth values, while the latter involves acquiring a series of object identifiers indicating server authentication and client authentication as an array.

Even when an unknown extension area is encountered, a robust fail-safe mechanism is implemented that continues decoding while preserving the raw data while checking for the presence of critical flags, and is designed to grasp the entire detailed attribute information without damaging the overall structure of the certificate.

Furthermore, for specialized extension areas such as certificate policy and institutional information access, the internal structure of each is recursively expanded to pinpoint information such as the uniform resource locator of the access destination.

To extract the public key information that forms the basis of a certificate's cryptographic strength, the engine first identifies the object identifier of the public key algorithm.

In the case of RSA encryption, key lengths such as 2048 bits and 4096 bits are specified by developing a composite ASN.1 structure consisting of a modulus and a public exponent and calculating the bit length of each.

On the other hand, in the case of elliptic curve cryptography, the identifier of the named curve being used is read and mapped to a specific curve name such as P-256 or P-384.

In addition, to analyze the signature value that ensures the validity of the certificate, we extract a signature algorithm that combines a hash function and public key cryptography, and prepare parameters to match the hash value of the certificate itself with the signature value.

These cryptographic parameters are recorded in great detail as structured data before being handed over to a cryptographic library as the basis for ensuring confidentiality and integrity of data along the communication path.

A mechanism has been built in which the extracted key data is converted into a format that can be used directly as an input value in the subsequent system's encryption processing and signature verification processing, and is provided to higher-level applications while completely preserving the cryptographic characteristics of the certificate.

When handling certificate data that requires a high level of security, our system does not send any input manuscript data to an external server, and uses a local processing method that is completed within the client-side web browser.

Complex hierarchical data decoded by the analysis engine is mapped as an intuitive structured tree view on the user interface.

This tree view is built as collapsible nodes that mirror the nested structure of ASN.1, allowing users to explore data at any depth, from certificate information at the top level to individual extended attributes at the bottom.

Additionally, it includes the ability to export all extracted decoded results as a single JSON document while preserving its hierarchical structure for reuse as input to system integration and automation tools, providing a standard data format for bulk validation using external scripts and seamless integration into configuration management systems.

Client-side processing utilizes the latest web assembly technology, making it possible to complete decoding asynchronously and at high speed without blocking the browser's drawing thread, even when processing large certificate files or multiple certificate chains at once.

A practical use case for this decoding tool is a rigorous pre-verification process before installing a certificate on a web server.

Users feed the issued PEM-formatted certificate string into the tool and visually verify that the intended common name and principal alternative name are set correctly and that all fully qualified domain names of interest are covered.

It also prevents communication errors by verifying that the start date of the validity period is in the past than the current time, that the end date accurately reflects the requested period, and that the key usage extension is appropriately flagged for digital signatures and key encryption.

By performing a series of verification tasks like this on a graphical screen, it is possible to eliminate the human errors associated with verification tasks using command line tools, and to establish a strong quality assurance process that minimizes the risk of service outages due to incomplete certificate information.

In addition, by leveraging the ability to simulate intermediate and root certificate hierarchies, you can logically check that the trust chain is correctly constructed before installation, serving as a comprehensive test environment to support secure deployment to production environments.