feat: check column configuration against encrypted column before decrypt

Author: tobyhede

docs/errors.md

@@ -21,6 +21,7 @@
   - [Unknown column](#encrypt-unknown-column)
   - [Unknown table](#encrypt-unknown-table)
   - [Unknown index term](#encrypt-unknown-index-term)
+  - [Column configuration mismatch](#encrypt-column-config-mismatch)
 
 - Decrypt errors:
    - [Column could not be deserialised](#encrypt-column-could-not-be-deserialised)
@@ -392,6 +393,34 @@ Unknown Index Term for column '{column_name}' in table '{table_name}'.
 
 
 <!-- ---------------------------------------------------------------------------------------------------- -->
+<!-- ---------------------------------------------------------------------------------------------------- -->
+
+
+## Column configuration mismatch <a id='encrypt-column-config-mismatch'></a>
+
+A returned encrypted column does not match the column configuration.
+
+### Error message
+
+```
+Column configuration for column '{column_name}' in table '{table_name}' does not match the encrypted column.
+```
+
+### Notes
+
+CipherStash Proxy validates that encrypted columns match the configuration before decrypting any data.
+If the table and column are not the same, this error is returned.
+The check is there to help prevent "confused deputy" issues and the error should *never* appear during normal operation.
+
+If the error persists, please contact CipherStash [support](https://cipherstash.com/support).
+
+
+### Further reading
+
+[AWS: The confused deputy problem](https://docs.aws.amazon.com/IAM/latest/UserGuide/confused-deputy.html)
+[Wikipedia: Confused deputy problem](https://en.wikipedia.org/wiki/Confused_deputy_problem)
+
+<!-- ---------------------------------------------------------------------------------------------------- -->
 
 
 

docs/how-to.md

@@ -163,7 +163,7 @@ This will output the version of EQL installed.
 In your existing PostgreSQL database, you store your data in tables and columns.
 Those columns have types like `integer`, `text`, `timestamp`, and `boolean`.
 When storing encrypted data in PostgreSQL with Proxy, you use a special column type called `eql_v1_encrypted`, which is [provided by EQL](#setting-up-the-database-schema).
-`eql_v1_encrypted` is a container column type that can be used for any type of encrypted data you want to store or search, whether they are numbers (`int`, `small_int`, `big_int`), text (`text`), dates and times (`date`), or booleans (`boolean`).
+`eql_v1_encrypted` is a container column type that can be used for any type of encrypted data you want to store or search, whether they are numbers (`int`, `small_int`, `big_int`), text (`text`), dates and times (`date`. `timestamp`), or booleans (`boolean`).
 
 Create a table with an encrypted column for `email`:
 

packages/cipherstash-proxy/src/error.rs

@@ -214,6 +214,9 @@ pub enum EncryptError {
     #[error("Column '{column}' in table '{table}' could not be encrypted. For help visit {}#encrypt-column-could-not-be-encrypted", ERROR_DOC_BASE_URL)]
     ColumnCouldNotBeEncrypted { table: String, column: String },
 
+    #[error("Column configuration for column '{column}' in table '{table}' does not match the encrypted column. For help visit {}#encrypt-column-config-mismatch", ERROR_DOC_BASE_URL)]
+    ColumnConfigurationMismatch { table: String, column: String },
+
     /// This should in practice be unreachable
     #[error("Missing encrypt configuration for column type `{plaintext_type}`. For help visit {}#encrypt-missing-encrypt-configuration", ERROR_DOC_BASE_URL)]
     MissingEncryptConfiguration { plaintext_type: String },

packages/cipherstash-proxy/src/postgresql/backend.rs

@@ -7,8 +7,8 @@ use super::messages::BackendCode;
 use crate::connect::Sender;
 use crate::encrypt::Encrypt;
 use crate::eql::EqlEncrypted;
-use crate::error::Error;
-use crate::log::{DEVELOPMENT, MAPPER, PROTOCOL};
+use crate::error::{EncryptError, Error};
+use crate::log::{DECRYPT, DEVELOPMENT, MAPPER, PROTOCOL};
 use crate::postgresql::context::Portal;
 use crate::postgresql::messages::data_row::DataRow;
 use crate::postgresql::messages::param_description::ParamDescription;
@@ -270,6 +270,34 @@ where
 
         let start = Instant::now();
 
+        for (col, ct) in projection_columns.iter().zip(&ciphertexts) {
+            debug!(target: DECRYPT, client_id = self.context.client_id, ?col, ?ct);
+
+            match (col, ct) {
+                (Some(col), Some(ct)) => {
+                    if col.identifier != ct.identifier {
+                        return Err(EncryptError::ColumnConfigurationMismatch {
+                            table: col.identifier.table.to_owned(),
+                            column: col.identifier.column.to_owned(),
+                        }
+                        .into());
+                    }
+                }
+                // configured column with NULL ciphertext
+                (Some(_), None) => {}
+                // unconfigured column *should* have no ciphertext,
+                (None, None) => {}
+                // ciphertext with no column configuration is bad
+                (None, Some(ct)) => {
+                    return Err(EncryptError::ColumnConfigurationMismatch {
+                        table: ct.identifier.table.to_owned(),
+                        column: ct.identifier.column.to_owned(),
+                    }
+                    .into());
+                }
+            }
+        }
+
         // Decrypt CipherText -> Plaintext
         let plaintexts = self.encrypt.decrypt(ciphertexts).await.inspect_err(|_| {
             counter!(DECRYPTION_ERROR_TOTAL).increment(1);