{"id":3079,"date":"2026-10-14T15:31:50","date_gmt":"2026-10-14T10:01:50","guid":{"rendered":"https:\/\/www.smsgatewaycenter.com\/blog\/?p=3079"},"modified":"2026-10-14T15:31:53","modified_gmt":"2026-10-14T10:01:53","slug":"sms-message-encryption-aes-wire-format-key-handling","status":"publish","type":"post","link":"https:\/\/www.smsgatewaycenter.com\/blog\/sms-message-encryption-aes-wire-format-key-handling\/","title":{"rendered":"SMS Message Encryption: What It Hides, What It Doesn’t, and How to Get the Wire Format Right"},"content":{"rendered":"\n

SMS message encryption<\/strong> keeps your message text out of the platform’s database, logs and reports, but the operator and the handset still see plaintext. Here’s the exact AES-CBC wire format, working code in four languages, the form-encoding and key-length traps that break interop, and how to rotate keys without losing your history.<\/p>\n\n\n\n

\"Abstract<\/a>
Encryption changes what the platform stores, not what the handset reads.<\/figcaption><\/figure>\n\n\n\n

Table of Contents<\/h1>\n\n\n\n
    \n
  1. The Short Answer<\/a><\/li>\n\n\n\n
  2. TL;DR<\/a><\/li>\n\n\n\n
  3. What Encryption Actually Hides<\/a><\/li>\n\n\n\n
  4. The Three Switches in the Portal<\/a><\/li>\n\n\n\n
  5. The Wire Format, Byte by Byte<\/a><\/li>\n\n\n\n
  6. The Two Endpoints: SMSApi\/encrypt and SMSApi\/decrypt<\/a><\/li>\n\n\n\n
  7. Encrypt Locally, Not Over the API<\/a><\/li>\n\n\n\n
  8. Sending an Encrypted Message<\/a><\/li>\n\n\n\n
  9. The Plus Sign That Breaks Everything<\/a><\/li>\n\n\n\n
  10. Key Length and Which Cipher You Get<\/a><\/li>\n\n\n\n
  11. Four Implementations, Four Traps<\/a><\/li>\n\n\n\n
  12. Proving Interop With a Canary<\/a><\/li>\n\n\n\n
  13. Length, Segments and Cost<\/a><\/li>\n\n\n\n
  14. Reading Encrypted Reports Back<\/a><\/li>\n\n\n\n
  15. Key Storage and the Key Ring<\/a><\/li>\n\n\n\n
  16. Rotating a Key Without Losing History<\/a><\/li>\n\n\n\n
  17. What the Format Doesn’t Protect<\/a><\/li>\n\n\n\n
  18. Encryption and the Rest of Your Pipeline<\/a><\/li>\n\n\n\n
  19. Decision Matrix<\/a><\/li>\n\n\n\n
  20. Pre-Launch Checklist<\/a><\/li>\n\n\n\n
  21. Unspecified Behaviour and How to Code Around It<\/a><\/li>\n\n\n\n
  22. FAQs<\/a><\/li>\n<\/ol>\n\n\n\n

    The Short Answer<\/h2>\n\n\n\n

    SMS message encryption<\/strong> on SMSGatewayCenter<\/strong> keeps the text of your messages out of the platform’s database, system logs, portal screens and downloaded reports. It doesn’t hide the text from the mobile operator or the person reading the SMS, and it can’t: the platform decrypts each message just before it hands it to the operator, because a handset can’t do anything with ciphertext.<\/p>\n\n\n\n

    The format is simple once you see it. Take 16 ASCII hex characters as the IV, AES-CBC encrypt the UTF-8 text with PKCS#7 padding and your secret token as the key, glue the IV to the front of the ciphertext, and base64 the lot. Do that in your own code, send it as msg<\/code> with encrypt=true<\/code>, and form-encode the body properly, because a base64 +<\/code> that turns into a space is the single most common way this breaks.<\/p>\n\n\n\n

    TL;DR<\/h2>\n\n\n\n