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| -rw-r--r-- | crypto-anastasis.rst | 33 |
1 files changed, 17 insertions, 16 deletions
diff --git a/crypto-anastasis.rst b/crypto-anastasis.rst index a73d31e..9b154a9 100644 --- a/crypto-anastasis.rst +++ b/crypto-anastasis.rst @@ -23,9 +23,9 @@ Specification of Cryptography in Anastasis ========================================== This document specifies the Crypto used in Anastasis. -------------------- -1. Key derivations -------------------- +--------------- +Key derivations +--------------- EdDSA and ECDHE public keys are always points on Curve25519 and represented using the standard 256 bit Ed25519 compact format. The binary representation @@ -61,8 +61,8 @@ likely also be available to other actors. **keysize**: The desired output size of the KDF, here 32 bytes. -1.1 Verification -^^^^^^^^^^^^^^^^ +Verification +^^^^^^^^^^^^ For users to authorize **policy** operations we need an EdDSA key pair. As we cannot assure that the corresponding private key is truly secret, such policy @@ -105,8 +105,8 @@ kdf_id. **eddsa_pub**: The generated EdDSA public key. -1.2 Encryption -^^^^^^^^^^^^^^ +Encryption +^^^^^^^^^^ For symmetric encryption of data we use AES256-GCM. For this we need a symmetric key and an initialization vector (IV). To ensure that the @@ -130,35 +130,36 @@ key material using an HKDF over a nonce and the kdf_id. **nonce**: 32-byte nonce, must never match "ver" (which it cannot as the length is different). **key**: Symmetric key which is later used to encrypt the documents with AES256-GCM. - + **iv**: IV which will be used for AES-GCM ---------------------------- -2. Key Usage +Key Usage ---------------------------- The keys we have generated, are now used to encrypt the recovery_document and the key_share of the user. -2.1 Encryption -^^^^^^^^^^^^^^ + +Encryption +^^^^^^^^^^ Before every encryption a 32-byte nonce is generated. From this the symmetric key is computed as described above. We use AES256-GCM for the encryption of the recovery_document and -key_share. +key_share. .. code-block:: tsref (encrypted_recovery_document, aes_gcm_tag) = AES256_GCM(recovery_document, key, iv) (encrypted_key_share, aes_gcm_tag) = AES256_GCM(key_share, key, iv) -**encrypted_recovery_document**: The encrypted RecoveryDocument (recovery_document) which contains the policies. +**encrypted_recovery_document**: The encrypted RecoveryDocument (recovery_document) which contains the policies. **encrypted_key_share**: The encrypted KeyShare (key_share). -2.2 Signatures -^^^^^^^^^^^^^^ +Signatures +^^^^^^^^^^ The EdDSA keys are used to sign the data sent from the client to the server. Everything the client sends to server is signed. The following algorithm is equivalent for **Anastasis-Policy-Signature**. @@ -168,7 +169,7 @@ server. Everything the client sends to server is signed. The following algorithm (anastasis-account-signature) = eddsa_sign(h_body, eddsa_priv) ver_res = eddsa_verifiy(h_body, anastasis-account-signature, eddsa_pub) -**anastasis-account-signature**: Signature over the hash of body. +**anastasis-account-signature**: Signature over the hash of body. **h_body**: The hashed body. |