From ca9b1900e305db08099d6b22f3144f6093131ae5 Mon Sep 17 00:00:00 2001
From: Alex Auvolat <alex@adnab.me>
Date: Wed, 18 May 2022 23:33:08 +0200
Subject: Add information about cryptography to readme

---
 README.md | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 110 insertions(+)
 create mode 100644 README.md

(limited to 'README.md')

diff --git a/README.md b/README.md
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+# Mailrage - Encrypted e-mail storage over Garage
+
+## Bayou storage module
+
+Checkpoints are stored in S3 at `<path>/checkpoint/<timestamp>`. Example:
+
+```
+348 TestMailbox/checkpoint/00000180d77400dc126b16aac546b769
+369 TestMailbox/checkpoint/00000180d776e509b68fdc5c376d0abc
+357 TestMailbox/checkpoint/00000180d77a7fe68f4f76e3b45aa751
+```
+
+Operations are stored in K2V at PK `<path>`, SK `<timestamp>`. Example:
+
+```
+TestMailbox 00000180d77400dc126b16aac546b769 RcIsESv7WrjMuHwyI/dvCnkIfy6op5Tiylf0WSnn94aMS2uagl7YeMBwdv09TiSXBpu5nJ5e/9QFSfuEI/NqKrdQkX54MOsnaIGhRb0oqUG3KNaar3BiVSvYvXuzYhk4ii+TUS2Eyd6fCCaNVNM5
+TestMailbox 00000180d775f27f5542a13fc21c665e RrTSOup/zO1Ei+QrjBcDLt4vvFSY+WJPBodwY64wy2ftW+Oh3VSArvlO4SAEPmdsx1gt0HPBZYR/OkVWsZpmix1ZLFUmvdib+rjNkorHQW1p+oLVK8tolGrqk4SRwl88cqu466T4vBEpDu7tRbH0
+TestMailbox 00000180d775f292b3c8da00718389b4 VAwd8SRycIwsipZW5AcSG+EIYZVWn/Uj/TADbWhb4x5LVMceiRBHWVquY08RgT/lJKdhIcUqBA15bVG3klIg8tLsWJVG784NbsZwdGRczWmngcA=
+TestMailbox 00000180d775f29d24842cf375d679e0 /FbXtEwm/bijtvOdqM1XFvKUalQFAOPHp+vF9jZThZn/viY5a6W1PyHeI8kTusF6EsVPAwPHpQyjIv/ghskC0f+zUEsSUhDwQANdwLNqDLAvTA==
+TestMailbox 00000180d7768ab1dc01ff504e887c62 W/fF0WitpxJ05yHeOv96BlpGymT1kVOjkIW00t9e6UE7mxkvNflu9cZSCd8PDJd2ymC0sC9bLVFAXKmNZsmCFEEHMQSyrX61qTYo4KFCZMp5zm6fXubaYuurrzjXzfUP/R7kBvICFZlF0daf0SwX
+TestMailbox 00000180d7768aba629c7ad6adf25228 IPzYGNsSepCX2AEnee/1Eas9a3c5esPSmrNkvaj4XcFb6Ft2KC8N6ubUR3wB+K0oYCTQym6nhHG5dlAxf6NRu7Rk8YtBTBmSqtGqd6kMZ3bU5b8=
+TestMailbox 00000180d7768ac1870cda61784114d4 aaLiaWxfx1mxh6aoKE3xUUfZWhivZ/K7ixabflFDW7FO/qbpvCaa+Y6w4lQemTy6m+leAhXGN+Dbyv2qP20yJ9O4oJF5d3Lz5Iv5uF18OxhVZzw=
+TestMailbox 00000180d776e4fb294ccdab2612b406 EtUPrLgEeOyab2QRnSie4I3Me9dDh10UdwWnUKdGa/8ezMJDtiy7XlW+tUfJdqtu6Vj7nduT0emDOXbBZsNwlcmzgYNwuNu3I9AfhZTFWtwLgB+wnAgB/jim82DDrJfLia8kB2eA2ao5jfJ3uMSZ
+TestMailbox 00000180d776e501528546d340490291 Lz4Z9wCTk1lZ86lL01urhAan4oHcr1NBqdRe+CDpA51D9IncA5+Fhc8I6knUIh2qQ5/woWgISLAVwzSS+0+TxrYoqxf5FumIQtUJfwDER5La3n0=
+TestMailbox 00000180d776e509b68fdc5c376d0abc RUGE2xB3fFX/wRH/p2fHIUa+rMaXSRd7fY9zglw0pRfVPqJfpniOjAe4GHIwGlwbwjtFOwS5a+Q7yr0Wez6QwD+ohhqRFKpbjcFcN7VfMyVAf+k=
+TestMailbox 00000180d7784b987a8ad8106dc400c9 K+0LVEtBbTnWNS67jy9DtTvQyd5arovduvu490tLOE2TzVhuVoF4pfvTMTN12bH3KwEAHeDfuwKkKJFqldOywouTYPzEjZFkJzyagHrkl6dfnE5CqmlDv+Vc5TOQRskxjW+wQiZdjU8wGiBiBGYh
+TestMailbox 00000180d7784bede69ac3cff2c6b724 XMFY3+b1r1//uolVz80JSI3g/84XCk3Tm7/S0BFv+Qe/Xv3/poLrOvAKEe+GzD2s22j8p/T2RXR/JSZckzgjEZeO0wbPDXVQd94di2Pff7jxAH8=
+TestMailbox 00000180d7784bffe2595abe7ed81858 QQZhF+7wSHfikoAp93a+UY/XDIX7TVnnVYOtmQ2XHnDKA2F6snRJCPbYBO4IRHCRfVrjDGi32c41it2C3Mu5PBepabxapsW1rfIV3rlX2lkKHtI=
+TestMailbox 00000180d77a7fb3f01dbb147c20cf7f IHOlOa1JI11RUKVvQUq3HQPxiRr4UCeE+pHmL8DtNMkOh62V4spuP0VvvQTJCQcPQ1EQR/QcxZ3s7uHLkrZAHF30BkpUkGqsLBWpnyug/puhdiixWsMyLLb6G90zFjiComUwptnDc/CCXtGEHdSW
+TestMailbox 00000180d77a7fbb54b100f521ceb347 Ze4KyyTCgrYbZlXlJSY5hNob8sMXvBAmwIx2cADbX5P0M1IHXwXfloEzvvd6WYOtatFC2GnDSrmQ6RdCfeZ3WV9TZilqa0Fv0XEg48sVyVCcguw=
+TestMailbox 00000180d77a7fe68f4f76e3b45aa751 cJJVvvRzTVNKUaIHPCCDY2uY7/HlmkxGgo3ozWBlBSRDeBqU65zgZD3QIPCxa6xaqB/Gc0bQ9BGzfU0cvVmO5jgNeeDnbqqs3oeA2jml/Qv2YO9upApfNQtDT1GiwJ8vrgaIow==
+TestMailbox 00000180d8e513d3ea58c679a13178ac Ce5su2YOxNmTzk2dK8SX8V/Uue5uAC7oklEjhesY9wCMqGphhOkdWjzCqq0xOzcb/ZzzZ58t+mTksNSYIU4kddHIHBFPgqIwKthVk2mlUdqYiN/Y2vEGqv+YmtKY+GST/7Ee87ZHpU/5sv0GoXxT
+TestMailbox 00000180d8e5145a23f8faee86283900 sp3D8xFZcM9icNlDJXIUDJb3mo6VGD9f1aDHD+4RbPdx6mTYF+qNTsPHKCxHHxT/9NfNe8XPg2+8xYRtm7SXfgERZBDB8ye+Xt3fM1k+wbL6RsaJmDHVECeXeL5KHuITzpI22A==
+TestMailbox 00000180d8e51465c38f0585f9bb760e FF0VId2O/bBNzYD5ABWReMs5hHoHwynOoJRKj9vyaUMZ3JykInFmvvRgtCbJBDjTQPwPU8apphKQfwuicO76H7GtZqH009Cbv5l8ZTRJKrmzOQmtjzBQc2eGEUMPfbml5t0GCg==
+```
+
+The timestamp of a checkpoint corresponds to the timestamp of the first operation NOT included in the checkpoint.
+In other words, to reconstruct the final state:
+
+- find timestamp `<ts>` of last checkpoint
+- load checkpoint `<ts>`
+- load and apply all operations starting from `<ts>`, included
+
+## UID index
+
+The UID index is an application of the Bayou storage module
+used to assign UID numbers to e-mails.
+See document we sent to NGI for properties on UIDVALIDITY.
+
+## Cryptography; key management
+
+Keys that are used:
+
+- master secret key (for indexes)
+- curve25519 public/private key pair (for incoming mail)
+
+Keys that are stored in K2V under PK `keys`:
+
+- `public`: the public curve25519 key (plain text)
+- `salt`: the 32-byte salt `S` used to calculate digests that index keys below
+- if a password is used, `password:<truncated(128bit) argon2 digest of password using salt S>`:
+  - a 32-byte salt `Skey`
+  - followed a secret box
+  - that is encrypted with a strong argon2 digest of the password (using the salt `Skey`)
+  - that contains the master secret key and the curve25519 private key
+- if recovery passwords are available, `recovery:<truncated digest>`: the same as for passwords
+
+Operations:
+
+- **Initialize**(`password`):
+  - generate salt `S` (32 random bytes)
+  - write `S` at `"salt"`
+  - `write("salt", S)`
+  - generate `public`, `private` (curve25519 keypair)
+  - generate `master` (secretbox secret key)
+  - calculate `digest = argon2_S(password)`
+  - generate salt `Skey` (32 random bytes)
+  - calculate `key = argon2_Skey(password)`
+  - serialize `box_contents = (private, master)`
+  - seal box `blob = seal_key(box_contents)`
+  - write `concat(Skey, blob)` at `"password:{hex(digest[..16])}"`
+
+- **Open**(`password`):
+  - load `S = read("salt")`
+  - calculate `digest = argon2_S(password)`
+  - load `blob = read("password:{hex(digest[..16])}")
+  - set `Skey = blob[..32]`
+  - calculate `key = argon2_Skey(password)`
+  - open secret box `box_contents = open_key(blob[32..])`
+  - retrieve `master` and `private` from `box_contents`
+  - retrieve `public = read("public")`
+
+- **ChangePassword**(`old_password`, `new_password`):
+  - load `S = read("salt")`
+  - calculate `digest = argon2_S(old_password)`
+  - load `blob = read("old_password:{hex(digest[..16])}")
+  - set `Skey = blob[..32]`
+  - calculate `key = argon2_Skey(old_password)`
+  - open secret box `box_contents = open_key(blob[32..])`
+  - retrieve `master` and `private` from `box_contents`
+
+  - calculate `digest_new = argon2_S(new_password)`
+  - generate salt `Skeynew` (32 random bytes)
+  - calculate `key_new = argon2_Skeynew(new_password)`
+  - serialize `box_contents_new = (private, master)`
+  - seal box `blob_new = seal_key_new(box_contents_new)`
+  - write `concat(Skeynew, blob_new)` at `"new_password:{hex(digest_new[..16])}"`
+  - delete `"old_password:{hex(digest[..16])}"`
+
+- **ResetPassword**(`recovery_key`, `new_password`): same as ChangePassword
-- 
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