# Mobile bid encryption contract

The mobile client uses the server-issued envelope key `K` for all bid
submissions. For text values, encrypt with AES-128/ECB/PKCS5 using the first
16 bytes of SHA-256(`K`) and send Base64 ciphertext. For the Envelope-C BOQ,
encrypt the raw workbook bytes with AES-128/ECB/PKCS5 using the first 16 bytes
of SHA-1(`K`) and upload the raw ciphertext bytes as the multipart `file`.

The same `K` must be sent as `randomKeyGenerated` and RSA-wrapped with every
officer/contractor public key in `saveEnvelopesOfficersDetailsResDTO`.

Envelope-C `requestDto` includes `deviceType: "Mobile"`, `fieldValue`,
`fieldValueInWord`, `hashValue` (SHA-256 of the unencrypted workbook bytes),
`fileName`, and the wrapped officer keys. The workbook editor preserves the
source workbook structure and only applies permitted cell edits.