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mukul975
88 lines
3.0 KiB
Markdown
88 lines
3.0 KiB
Markdown
# Workflows - End-to-End Encryption for Messaging
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## Workflow 1: X3DH Key Agreement
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```
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Alice (initiator) Server Bob (responder)
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| |<-- Register: |
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| | Identity Key (IK_B) |
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| | Signed PreKey (SPK_B)|
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| | One-Time PreKeys |
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|-- Fetch Bob's Keys ----------->| |
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|<-- IK_B, SPK_B, OPK_B --------| |
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[Compute shared secret]: |
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DH1 = DH(IK_A, SPK_B) |
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DH2 = DH(EK_A, IK_B) |
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DH3 = DH(EK_A, SPK_B) |
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DH4 = DH(EK_A, OPK_B) |
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SK = HKDF(DH1 || DH2 || DH3 || DH4) |
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|-- Send Initial Message ------->|-- Forward to Bob ------>|
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| (IK_A, EK_A, OPK_id, msg) | |
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| | [Bob computes same SK]|
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```
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## Workflow 2: Double Ratchet (Sending)
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```
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[Message to Send]
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[Check: Do we have recipient's new DH public key?]
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YES --> [DH Ratchet Step]
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- Generate new DH key pair
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- Compute DH shared secret
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- Derive new root key + sending chain key via HKDF
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NO --> [Continue with current sending chain]
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[Symmetric Ratchet: Derive message key from sending chain]
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(chain_key, message_key) = HMAC(chain_key, constants)
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[Encrypt message with AES-256-GCM using message_key]
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[Include header: DH public key, previous chain length, message number]
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[Delete message_key from memory]
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```
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## Workflow 3: Double Ratchet (Receiving)
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```
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[Received Encrypted Message + Header]
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[Check DH public key in header]
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[New key?]
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YES --> [DH Ratchet Step]
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- Compute DH shared secret
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- Derive new root key + receiving chain key
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NO --> [Use current receiving chain]
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[Symmetric Ratchet: Derive message key]
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[Decrypt message with AES-256-GCM]
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[Verify authentication tag]
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FAIL --> Reject message
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PASS --> Return plaintext
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[Delete message_key from memory]
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```
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## Workflow 4: Session Lifecycle
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```
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[Initial Contact] --> [X3DH Key Exchange]
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[Initialize Double Ratchet]
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[Exchange Messages]
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(DH ratchet + symmetric ratchet)
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[Periodic DH Ratchet]
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(every N messages or on reply)
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[Session End / Archive]
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```
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