Secure the contents of the attachment.
You must encrypt an attachment before uploading it to Business Chat. To encrypt an attachment, do the following:
Encrypt the attachment using the AES/CTR/NoPadding algorithm with an all-zero, 16-byte initialization vector (IV).
Generate a single-use 256-bit AES decryption key using a cryptographically-secure random number generator, and not a weak source like
Store the key as a hex-encoded string, prefixed with
00, in the key field of the Attachment dictionary in the message JSON.