{"id":11297,"date":"2024-03-14T13:46:07","date_gmt":"2024-03-14T13:46:07","guid":{"rendered":"https:\/\/www.silicloud.com\/blog\/how-can-the-rsa-encryption-algorithm-be-implemented-in-the-c-language\/"},"modified":"2025-08-04T10:00:55","modified_gmt":"2025-08-04T10:00:55","slug":"how-can-the-rsa-encryption-algorithm-be-implemented-in-the-c-language","status":"publish","type":"post","link":"https:\/\/www.silicloud.com\/blog\/how-can-the-rsa-encryption-algorithm-be-implemented-in-the-c-language\/","title":{"rendered":"RSA Encryption in C: Step-by-Step Guide"},"content":{"rendered":"<p>Here is a simple example code in C language implementing the RSA encryption algorithm.<\/p>\n<pre class=\"post-pre\"><code><span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;stdio.h&gt;<\/span><\/span>\r\n<span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;stdlib.h&gt;<\/span><\/span>\r\n<span class=\"hljs-meta\">#<span class=\"hljs-keyword\">include<\/span> <span class=\"hljs-string\">&lt;math.h&gt;<\/span><\/span>\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">gcd<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">int<\/span> a, <span class=\"hljs-type\">int<\/span> b)<\/span> {\r\n    <span class=\"hljs-keyword\">if<\/span> (b == <span class=\"hljs-number\">0<\/span>)\r\n        <span class=\"hljs-keyword\">return<\/span> a;\r\n    <span class=\"hljs-keyword\">else<\/span>\r\n        <span class=\"hljs-keyword\">return<\/span> gcd(b, a % b);\r\n}\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">is_prime<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">int<\/span> n)<\/span> {\r\n    <span class=\"hljs-keyword\">if<\/span> (n &lt;= <span class=\"hljs-number\">1<\/span>)\r\n        <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n    <span class=\"hljs-keyword\">for<\/span> (<span class=\"hljs-type\">int<\/span> i = <span class=\"hljs-number\">2<\/span>; i &lt;= <span class=\"hljs-built_in\">sqrt<\/span>(n); i++) {\r\n        <span class=\"hljs-keyword\">if<\/span> (n % i == <span class=\"hljs-number\">0<\/span>)\r\n            <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n    }\r\n    <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">1<\/span>;\r\n}\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">generate_prime<\/span><span class=\"hljs-params\">()<\/span> {\r\n    <span class=\"hljs-type\">int<\/span> p;\r\n    <span class=\"hljs-keyword\">do<\/span> {\r\n        p = rand() % <span class=\"hljs-number\">100<\/span> + <span class=\"hljs-number\">1<\/span>;\r\n    } <span class=\"hljs-keyword\">while<\/span> (!is_prime(p));\r\n    <span class=\"hljs-keyword\">return<\/span> p;\r\n}\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">mod_exp<\/span><span class=\"hljs-params\">(<span class=\"hljs-type\">int<\/span> base, <span class=\"hljs-type\">int<\/span> <span class=\"hljs-built_in\">exp<\/span>, <span class=\"hljs-type\">int<\/span> mod)<\/span> {\r\n    <span class=\"hljs-type\">int<\/span> result = <span class=\"hljs-number\">1<\/span>;\r\n    <span class=\"hljs-keyword\">while<\/span> (<span class=\"hljs-built_in\">exp<\/span> &gt; <span class=\"hljs-number\">0<\/span>) {\r\n        <span class=\"hljs-keyword\">if<\/span> (<span class=\"hljs-built_in\">exp<\/span> % <span class=\"hljs-number\">2<\/span> == <span class=\"hljs-number\">1<\/span>)\r\n            result = (result * base) % mod;\r\n        base = (base * base) % mod;\r\n        <span class=\"hljs-built_in\">exp<\/span> \/= <span class=\"hljs-number\">2<\/span>;\r\n    }\r\n    <span class=\"hljs-keyword\">return<\/span> result;\r\n}\r\n\r\n<span class=\"hljs-type\">int<\/span> <span class=\"hljs-title function_\">main<\/span><span class=\"hljs-params\">()<\/span> {\r\n    <span class=\"hljs-type\">int<\/span> p = generate_prime();\r\n    <span class=\"hljs-type\">int<\/span> q = generate_prime();\r\n\r\n    <span class=\"hljs-type\">int<\/span> n = p * q;\r\n    <span class=\"hljs-type\">int<\/span> phi = (p - <span class=\"hljs-number\">1<\/span>) * (q - <span class=\"hljs-number\">1<\/span>);\r\n\r\n    <span class=\"hljs-type\">int<\/span> e = <span class=\"hljs-number\">2<\/span>;\r\n    <span class=\"hljs-keyword\">while<\/span> (gcd(e, phi) != <span class=\"hljs-number\">1<\/span>) {\r\n        e++;\r\n    }\r\n\r\n    <span class=\"hljs-type\">int<\/span> d = <span class=\"hljs-number\">1<\/span>;\r\n    <span class=\"hljs-keyword\">while<\/span> ((d * e) % phi != <span class=\"hljs-number\">1<\/span>) {\r\n        d++;\r\n    }\r\n\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Public key: (%d, %d)\\n\"<\/span>, e, n);\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Private key: (%d, %d)\\n\"<\/span>, d, n);\r\n\r\n    <span class=\"hljs-type\">int<\/span> plaintext = <span class=\"hljs-number\">123<\/span>;\r\n    <span class=\"hljs-type\">int<\/span> ciphertext = mod_exp(plaintext, e, n);\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Encrypted message: %d\\n\"<\/span>, ciphertext);\r\n\r\n    <span class=\"hljs-type\">int<\/span> decrypted_text = mod_exp(ciphertext, d, n);\r\n    <span class=\"hljs-built_in\">printf<\/span>(<span class=\"hljs-string\">\"Decrypted message: %d\\n\"<\/span>, decrypted_text);\r\n\r\n    <span class=\"hljs-keyword\">return<\/span> <span class=\"hljs-number\">0<\/span>;\r\n}\r\n<\/code><\/pre>\n<p>This code generates two random prime numbers, p and q, calculates the values of n and phi, selects a public key e and private key d, then encrypts plaintext using the public key and decrypts ciphertext using the private key. Please note that the encryption and decryption here are only for demonstration purposes and in real applications, larger prime numbers and more complex operations should be used.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>Here is a simple example code in C language implementing the RSA encryption algorithm. #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #include &lt;math.h&gt; int gcd(int a, int b) { if (b == 0) return a; else return gcd(b, a % b); } int is_prime(int n) { if (n &lt;= 1) return 0; for (int i = 2; i [&hellip;]<\/p>\n","protected":false},"author":8,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_import_markdown_pro_load_document_selector":0,"_import_markdown_pro_submit_text_textarea":"","footnotes":""},"categories":[1],"tags":[3190,381,14,7,14524],"class_list":["post-11297","post","type-post","status-publish","format-standard","hentry","category-uncategorized","tag-algorithm-implementation","tag-c-programming","tag-cryptography","tag-encryption","tag-rsa"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v21.5 (Yoast SEO v21.5) - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>RSA Encryption in C: Step-by-Step Guide - Blog - Silicon Cloud<\/title>\n<meta name=\"description\" content=\"Learn to implement RSA encryption algorithm in C with code examples. Master cryptography concepts &amp; secure programming practices.\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.silicloud.com\/blog\/how-can-the-rsa-encryption-algorithm-be-implemented-in-the-c-language\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"RSA Encryption in C: Step-by-Step Guide\" \/>\n<meta property=\"og:description\" content=\"Learn to implement RSA encryption algorithm in C with code examples. 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