Skip to content

Commit b244984

Browse files
javascript-2020javascript-2020
committed
save file
1 parent ae8519c commit b244984

1 file changed

Lines changed: 135 additions & 2 deletions

File tree

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

Lines changed: 135 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -227,6 +227,8 @@ <h3 class=blog-hdr>
227227
</div>
228228

229229

230+
231+
230232
<div class=blog-text>
231233
<h3 class=blog-hdr>
232234
PKCS#1 vs PKCS#8 (the important difference)
@@ -343,8 +345,9 @@ <h3 class=blog-hdr>
343345
<code>
344346
openssl pkcs8 -topk8 -nocrypt -in pkcs1.pem -out pkcs8.pem
345347
</code>
346-
347-
348+
</div>
349+
350+
348351
<div class=blog-text>
349352
<h3 class=blog-hdr>
350353
SPKI
@@ -445,6 +448,136 @@ <h4>
445448
</div>
446449

447450

451+
452+
453+
454+
<div class=blog-text>
455+
<h3>what size rsa keys do i need to encrypt an aes key of 256 bits</h3>
456+
<p>To safely encrypt a 256-bit AES key using RSA, you should use an RSA key size of at least 2048 bits,
457+
though 3072 bits or 4096 bits is highly recommended for modern applications requiring long-term security.</p>
458+
<p>The reason for this requires looking at how RSA and AES work together, as well as the strict physical limits of RSA encryption.</p>
459+
<p>In cryptography, you want the security strength of your asymmetric key (RSA) to match or exceed the security strength of your symmetric key (AES).</p>
460+
<p><strong>2048-bit RSA</strong> provides roughly <strong>112 bits</strong> of effective security strength (vulnerable to well-funded adversaries or long-term storage cracking over the next decade).</p>
461+
<p><strong>3072-bit RSA</strong> provides roughly <strong>128 bits</strong> of effective security strength (the current NIST recommended minimum for modern systems).</p>
462+
<p><strong>4096-bit RSA</strong> provides roughly <strong>140+ bits</strong> of effective security strength.</p>
463+
<p>While mathematically a 3072-bit or 4096-bit RSA key is technically required to get closer to the massive security margin of a 256-bit AES key,
464+
<strong>2048-bit is the absolute bare minimum</strong> allowed by modern cryptographic standards.</p>
465+
<h2>Padding Overhead</h2>
466+
<p>You can easily fit a 256-bit (32-byte) AES key into even the smallest standard RSA key size because of how RSA handles data.</p>
467+
<p>An RSA key can only encrypt data that is smaller than its own modulus size, minus the required bytes for secure padding (like OAEP).</p>
468+
<table>
469+
<thead>
470+
<tr>
471+
<th>RSA Key Size</th>
472+
<th>Max Total Capacity</th>
473+
<th>Padding Overhead (OAEP SHA-256)</th>
474+
<th>Max Allowed Payload Space</th>
475+
<th>Can it fit a 32-byte AES key?</th>
476+
</tr>
477+
</thead>
478+
<tbody>
479+
<tr>
480+
<td>1024-bit (Obsolete)</td>
481+
<td>128 bytes</td>
482+
<td>66 bytes</td>
483+
<td>62 bytes</td>
484+
<td>Yes (But insecure)</td>
485+
</tr>
486+
<tr>
487+
<td>2048-bit</td>
488+
<td>256 bytes</td>
489+
<td>66 bytes</td>
490+
<td>190 bytes</td>
491+
<td>Yes</td>
492+
</tr>
493+
<tr>
494+
<td>3072-bit</td>
495+
<td>384 bytes</td>
496+
<td>66 bytes</td>
497+
<td>318 bytes</td>
498+
<td>Yes</td>
499+
</tr>
500+
<tr>
501+
<td>4096-bit</td>
502+
<td>512 bytes</td>
503+
<td>66 bytes</td>
504+
<td>446 bytes</td>
505+
<td>Yes</td>
506+
</tr>
507+
</tbody>
508+
</table>
509+
<p>Even a 2048-bit RSA key gives you 190 bytes of payload space, which is more than enough room to slot your 32-byte AES key into.</p>
510+
<h2>Recommendation</h2>
511+
<p>Go with 3072-bit if you want the optimal balance between tight security and fast performance,
512+
or 4096-bit if execution time isn't a bottleneck in your application and you want maximum security.
513+
Avoid 2048-bit if you are designing a brand-new system from scratch.</p>
514+
515+
</div>
516+
517+
518+
<div class=blog-text>
519+
<h3>how does iv length affect things? whats the deal with 96 bits</h3>
520+
<p>When dealing with encryption (specifically symmetric encryption like <strong>AES</strong>), the <strong>Initialization Vector (IV)</strong>
521+
ensures that encrypting the exact same data twice results in two completely different ciphertexts.
522+
This prevents attackers from spotting patterns in your data.</p>
523+
<p>How the IV length affects things depends heavily on the <strong>encryption mode</strong> you are using.
524+
The &quot;96 bits&quot; sweet spot is tied directly to the most popular modern encryption mode: <strong>AES-GCM</strong>.</p>
525+
<p>Here is the breakdown of why IV length matters and what makes 96 bits special.</p>
526+
<h4>Why 96 Bits (12 Bytes) is the Golden Number</h4>
527+
<p>The 96-bit rule is specific to <strong>AES-GCM (Galois/Counter Mode)</strong>, which is the industry standard for authenticated encryption.</p>
528+
<p>When you use AES-GCM, the internal mechanism requires a <strong>128-bit block</strong> to work with. It splits that 128-bit block into two parts:</p>
529+
<ul>
530+
<li>
531+
<p>The IV : 96 bits.</p>
532+
</li>
533+
<li>
534+
<p>A Counter: 32 bits (which starts at 0000...0001 and increments for every block of data encrypted).</p>
535+
</li>
536+
</ul>
537+
<pre><code>AES-GCM Internal Block (128 bits total)
538+
+------------------------------------+------------------+
539+
| IV / Nonce | Counter |
540+
| (96 bits) | (32 bits) |
541+
+------------------------------------+------------------+
542+
</code></pre>
543+
<h4>What happens if you use a 96-bit IV?</h4>
544+
<p>If you supply exactly 96 bits, the cryptographic engine simply pads it with a 32-bit counter starting at 1.
545+
<strong>This is direct, incredibly fast, and requires zero extra computational overhead.</strong></p>
546+
<h4>What happens if you use any other size (e.g., 128 bits)?</h4>
547+
<p>If you pass an IV that is not 96 bits, the algorithm cannot use it directly. Instead, it has to run your IV through
548+
a hashing function called GHASH to mathematically compress or stretch it into a 96-bit value first.</p>
549+
<p>The Downside: This adds extra computation (hurting performance), can subtly introduce a higher risk of IV collisions,
550+
and can lead to implementation bugs across different programming languages.</p>
551+
<p>Rule of Thumb for GCM: Always use a 96-bit (12-byte) IV for AES-GCM. Using anything else is less efficient
552+
and prone to compatibility headaches.</p>
553+
<h4>What About Other Modes (Like AES-CBC)?</h4>
554+
<p>If you are using an older mode like AES-CBC (Cipher Block Chaining), the rule is different.</p>
555+
<p>CBC mode requires the IV to be exactly the same size as the cipher's block size.
556+
Since AES always has a block size of 128 bits, AES-CBC requires a 128-bit (16-byte) IV.</p>
557+
<p>If you give it a 96-bit IV, the code will throw an error or crash because it lacks the bytes
558+
needed to scramble the first block of data.</p>
559+
<h4>How IV Length Affects Security (The &quot;Birthday Paradox&quot;)</h4>
560+
<p>The length of your IV dictates how many unique messages you can safely encrypt using the same secret
561+
key before you risk repeating an IV. Repeating an IV with the same key is a catastrophic cryptographic failure.</p>
562+
<p>128-bit IV (CBC Mode): Extremely large space (2^128). You can safely generate random IVs for trillions of
563+
messages without ever worrying about a duplicate.</p>
564+
<p>96-bit IV (GCM Mode): While $2^{96}$ is still a massive number, the math behind random collisions
565+
(the Birthday Paradox) dictates that if you generate purely random 96-bit IVs, you shouldn't encrypt
566+
more than roughly (2^32) (about 4.2 billion) messages under a single key.</p>
567+
<h5>How to handle the 96-bit limit in GCM:</h5>
568+
<p>Because 96 bits is a bit tighter for random generation, cryptographic standards suggest two ways to stay safe:</p>
569+
<ul>
570+
<li>
571+
<p>The Counter Approach (Deterministic): Use a fixed 64-bit device ID combined with a 32-bit
572+
incrementing counter as your IV. Because it counts up, it will never repeat until the counter rolls over.</p>
573+
</li>
574+
<li>
575+
<p>Key Rotation: If you must use purely random 96-bit IVs, generate a fresh encryption key well before you hit a billion messages.</p>
576+
</li>
577+
</ul>
578+
579+
</div>
580+
448581
<log-mod component></log-mod>
449582

450583

0 commit comments

Comments
 (0)