Initial commit - 611 cybersecurity skills across all subdomains

2026-07-18 21:49:40 +03:00 · 2026-02-25 10:47:44 +01:00
commit 22a7ab1462
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+# Workflows - End-to-End Encryption for Messaging
+
+## Workflow 1: X3DH Key Agreement
+
+```
+Alice (initiator)                 Server                  Bob (responder)
+  |                                 |                         |
+  |                                 |<-- Register:            |
+  |                                 |    Identity Key (IK_B)  |
+  |                                 |    Signed PreKey (SPK_B)|
+  |                                 |    One-Time PreKeys     |
+  |                                 |                         |
+  |-- Fetch Bob's Keys ----------->|                         |
+  |<-- IK_B, SPK_B, OPK_B --------|                         |
+  |                                 |                         |
+  [Compute shared secret]:                                    |
+  DH1 = DH(IK_A, SPK_B)                                     |
+  DH2 = DH(EK_A, IK_B)                                      |
+  DH3 = DH(EK_A, SPK_B)                                     |
+  DH4 = DH(EK_A, OPK_B)                                     |
+  SK = HKDF(DH1 || DH2 || DH3 || DH4)                      |
+  |                                 |                         |
+  |-- Send Initial Message ------->|-- Forward to Bob ------>|
+  |   (IK_A, EK_A, OPK_id, msg)   |                         |
+  |                                 |   [Bob computes same SK]|
+```
+
+## Workflow 2: Double Ratchet (Sending)
+
+```
+[Message to Send]
+      |
+[Check: Do we have recipient's new DH public key?]
+  YES --> [DH Ratchet Step]
+          - Generate new DH key pair
+          - Compute DH shared secret
+          - Derive new root key + sending chain key via HKDF
+  NO  --> [Continue with current sending chain]
+      |
+[Symmetric Ratchet: Derive message key from sending chain]
+(chain_key, message_key) = HMAC(chain_key, constants)
+      |
+[Encrypt message with AES-256-GCM using message_key]
+      |
+[Include header: DH public key, previous chain length, message number]
+      |
+[Delete message_key from memory]
+```
+
+## Workflow 3: Double Ratchet (Receiving)
+
+```
+[Received Encrypted Message + Header]
+      |
+[Check DH public key in header]
+  [New key?]
+    YES --> [DH Ratchet Step]
+            - Compute DH shared secret
+            - Derive new root key + receiving chain key
+    NO  --> [Use current receiving chain]
+      |
+[Symmetric Ratchet: Derive message key]
+      |
+[Decrypt message with AES-256-GCM]
+      |
+[Verify authentication tag]
+  FAIL --> Reject message
+  PASS --> Return plaintext
+      |
+[Delete message_key from memory]
+```
+
+## Workflow 4: Session Lifecycle
+
+```
+[Initial Contact] --> [X3DH Key Exchange]
+                            |
+                      [Initialize Double Ratchet]
+                            |
+                      [Exchange Messages]
+                      (DH ratchet + symmetric ratchet)
+                            |
+                      [Periodic DH Ratchet]
+                      (every N messages or on reply)
+                            |
+                      [Session End / Archive]
+```