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‎blog/26-04-26/x509-certificates-in-js---encrypt-decrypt-data/x509-certificates-in-js---encrypt-decrypt-data.html‎

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@@ -81,16 +81,42 @@ <h1 class=title>
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<div class=description>
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<p>
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This blog post describes using x509 certificates to encrypt and decrypt data in a javascript environment. This
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This blog post describes using x509 certificates to encrypt and decrypt data in javascript environments. This
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can be useful since the public certificate can be made available publicly, even sent via an insecure communication
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channel, this public certificate can be used to encrypt data, the encrypted data can be sent to the holder
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of the private key, who can subsequently decode the encrypted data using the private key.
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<br>
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If two parties want to have a bi-directional encrypted communication, they can both send each other their
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public certificates.
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</p>
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</div>
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<div class=blog-text>
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<h4>
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notes :
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</h4>
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<p>
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Node.js supports both PKCS#1 and PKCS#8 private keys, while browsers only support PKCS#8.
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This difference comes from how each environment exposes cryptography: Node wraps OpenSSL
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(very flexible), while browsers expose WebCrypto (much stricter and standardized).
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private keys :
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</p>
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<ul>
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<li>
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Browsers only support PKCS#8
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</li>
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<li>
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Node.js supports both PKCS#1 and PKCS#8 private keys
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</li>
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</ul>
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<p>
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certificates :
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</p>
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<ul>
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<li>
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Browsers require the spki component in der form
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</li>
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<li>
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node.js supports the entire certificate in pem format
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</li>
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<snippet-editor component id=x509-nodejs src='ex/x509-nodejs.js'></snippet-editor>
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<divv class=blog-text>
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<h3 class=blog-hdr>
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SPKI
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</h3>
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<p>
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SPKI in X.509 stands for Subject Public Key Info.
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<br>
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It is the part of an X.509 certificate that contains the subject’s public key
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and information about the algorithm used with that key.
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</p>
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<h4>
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What SPKI actually contains
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</h4>
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<p>
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The Subject Public Key Info (SPKI) field is a structured ASN.1 block inside every X.509 certificate. It includes:
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</p>
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<ul>
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<li>
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The subject’s public key (e.g., RSA, ECDSA, Ed25519)
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</li>
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<li>
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The algorithm identifier for that key (e.g., rsaEncryption, id-ecPublicKey)
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</li>
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<li>
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Any algorithm parameters required by that key type
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</li>
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</ul>
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<p>
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This is the part of the certificate that clients use to verify signatures or establish encrypted sessions.
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</p>
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<h4>
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Why SPKI matters
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</h4>
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<p>
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SPKI is essential because:
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</p>
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<ul>
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It is the actual public key that the certificate binds to an identity.
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</li>
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<li>
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It is used by TLS, code signing, S/MIME, and other PKI systems to verify authenticity.
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</li>
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<li>
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It is the part that gets hashed when generating a certificate pin (HPKP-style pins or modern SPKI pinning in some systems).
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</li>
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</ul>
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<p>
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In short, SPKI is the cryptographic heart of the certificate.
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</p>
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<h4>
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Where SPKI sits in the certificate structure
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</h4>
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<p>
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According to the X.509 standard, SPKI is one of the core Version 1 certificate fields,
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meaning it has existed since the earliest form of the standard.
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<a href='https://learn.microsoft.com/en-us/azure/iot-hub/reference-x509-certificates'>
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</a>
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</p>
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<p>
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Typical X.509 structure (simplified):
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</p>
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<ul>
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<li>
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Version
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</li>
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<li>
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Serial Number
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</li>
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<li>
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Signature Algorithm
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</li>
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<li>
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Issuer
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</li>
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<li>
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Validity
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</li>
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<li>
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Subject
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</li>
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<li>
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Subject Public Key Info (SPKI)
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</li>
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<li>
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Extensions (v3)
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</li>
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<li>
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Signature
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</li>
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</ul>
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</div>
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<log-mod component></log-mod>

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