diff --git a/biscuit-auth/Cargo.toml b/biscuit-auth/Cargo.toml
index 4e100841..322cb555 100644
--- a/biscuit-auth/Cargo.toml
+++ b/biscuit-auth/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "biscuit-auth"
-version = "4.1.1"
+version = "5.0.0"
 description = "an authorization token with decentralized verification and offline attenuation"
 authors = ["Geoffroy Couprie <contact@geoffroycouprie.com>"]
 edition = "2018"
diff --git a/biscuit-auth/samples/README.md b/biscuit-auth/samples/README.md
index 0e61691a..e5fbafe3 100644
--- a/biscuit-auth/samples/README.md
+++ b/biscuit-auth/samples/README.md
@@ -1841,7 +1841,7 @@ allow if true;
 
 revocation ids:
 - `470e4bf7aa2a01ab39c98150bd06aa15b4aa5d86509044a8809a8634cd8cf2b42269a51a774b65d10bac9369d013070b00187925196a8e680108473f11cf8f03`
-- `93a7315ab1272da9eeef015f6fecbc9ac96fe4660e6204bf64ea2105ebe309e9c9cadc0a26c5604f13910fae3f2cd0800756afb6b6b208bf77adeb1ab2f42405`
+- `342167bc54bc642b6718a276875e55b6d39e9b21e4ce13b926a3d398b6c057fc436385bf4c817a16f9ecdf0b0d950e8b8258a20aeb3fd8896c5e9c1f0a53da03`
 
 authorizer world:
 ```
@@ -2041,7 +2041,7 @@ check if true trusting previous, ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755
 1:
 symbols: []
 
-public keys: ["ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463"]
+public keys: ["ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463", "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"]
 
 external signature by: "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"
 
@@ -2055,7 +2055,7 @@ check if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5
 2:
 symbols: []
 
-public keys: []
+public keys: ["ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463", "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"]
 
 external signature by: "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463"
 
@@ -2068,7 +2068,7 @@ check if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5
 3:
 symbols: []
 
-public keys: []
+public keys: ["ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463", "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"]
 
 external signature by: "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463"
 
@@ -2081,7 +2081,7 @@ check if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5
 4:
 symbols: []
 
-public keys: ["ed25519/f98da8c1cf907856431bfc3dc87531e0eaadba90f919edc232405b85877ef136"]
+public keys: ["ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463", "ed25519/f98da8c1cf907856431bfc3dc87531e0eaadba90f919edc232405b85877ef136"]
 
 ```
 query(4);
@@ -2103,10 +2103,10 @@ allow if true;
 
 revocation ids:
 - `3771cefe71beb21ead35a59c8116ee82627a5717c0295f35980662abccb159fe1b37848cb1818e548656bd4fd882d0094a2daab631c76b2b72e3a093914bfe04`
-- `45133b90f228a81fe4d3042a79f6c6b7608e656e903d6b1f4db32cd774b09b8315af360879a5f210ad7be37ff55e3eb34f237bcc9711407b6329ac6018bfb400`
-- `179f054f3c572646aba5013159ae192ac42f5666dbdd984129955f4652b6829e59f54aa251e451f96329d42a2524ce569c3e1ec52e708b642dd8994af51dd703`
-- `edab54789d6656936fcd28200b9c61643434842d531f09f209fad555e11ff53174db174dafba126e6de448983a56f78d2042bc5782d71a45799c022fe69fb30d`
-- `6a62306831e9dbe83e7b33db96b758c77dd690930f2d2d87e239b210b1944c5582bf6d7e1bfea8e7f928c27f2fff0e2ee2e0adc41e11e0c3abe8d7b96b9ede07`
+- `6528db2c9a561ada9086268549a600a8a52ff434ea8183812623eec0e9b6c5d3c41ab7868808623021d92294d583afdf92f4354bcdaa1bc50453e1b89afd630d`
+- `5d5679fe69bfe74b7919323515e9ecba9d01422b16be9341b57f88e695b2bb0bd7966b781001d2b9e00ee618fdc239c96e17e32cb379f13f12d6bd7b1b47ad04`
+- `c37bf24c063f0310eccab8864e48dbeffcdd7240b4f8d1e01eba4fc703e6c9082b845bb55543b10f008dc7f4e78540411912ac1f36fa2aa90011dca40f323b09`
+- `3f675d6c364e06405d4868c904e40f3d81c32b083d91586db814d4cb4bf536b4ba209d82f11b4cb6da293b60b20d6122fc3e0e08e80c381dee83edd848211900`
 
 authorizer world:
 ```
diff --git a/biscuit-auth/samples/samples.json b/biscuit-auth/samples/samples.json
index acae28a8..d97790a7 100644
--- a/biscuit-auth/samples/samples.json
+++ b/biscuit-auth/samples/samples.json
@@ -1798,7 +1798,7 @@
           "authorizer_code": "allow if true;\n",
           "revocation_ids": [
             "470e4bf7aa2a01ab39c98150bd06aa15b4aa5d86509044a8809a8634cd8cf2b42269a51a774b65d10bac9369d013070b00187925196a8e680108473f11cf8f03",
-            "93a7315ab1272da9eeef015f6fecbc9ac96fe4660e6204bf64ea2105ebe309e9c9cadc0a26c5604f13910fae3f2cd0800756afb6b6b208bf77adeb1ab2f42405"
+            "342167bc54bc642b6718a276875e55b6d39e9b21e4ce13b926a3d398b6c057fc436385bf4c817a16f9ecdf0b0d950e8b8258a20aeb3fd8896c5e9c1f0a53da03"
           ]
         }
       }
@@ -1939,26 +1939,34 @@
         {
           "symbols": [],
           "public_keys": [
-            "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463"
+            "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
+            "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"
           ],
           "external_key": "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189",
           "code": "query(1);\nquery(1, 2) <- query(1), query(2) trusting ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463;\ncheck if query(2), query(3) trusting ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463;\ncheck if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189;\n"
         },
         {
           "symbols": [],
-          "public_keys": [],
+          "public_keys": [
+            "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
+            "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"
+          ],
           "external_key": "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
           "code": "query(2);\ncheck if query(2), query(3) trusting ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463;\ncheck if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189;\n"
         },
         {
           "symbols": [],
-          "public_keys": [],
+          "public_keys": [
+            "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
+            "ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189"
+          ],
           "external_key": "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
           "code": "query(3);\ncheck if query(2), query(3) trusting ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463;\ncheck if query(1) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189;\n"
         },
         {
           "symbols": [],
           "public_keys": [
+            "ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463",
             "ed25519/f98da8c1cf907856431bfc3dc87531e0eaadba90f919edc232405b85877ef136"
           ],
           "external_key": null,
@@ -2082,10 +2090,10 @@
           "authorizer_code": "check if query(1, 2) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189, ed25519/a060270db7e9c9f06e8f9cc33a64e99f6596af12cb01c4b638df8afc7b642463;\n\ndeny if query(3);\ndeny if query(1, 2);\ndeny if query(0) trusting ed25519/acdd6d5b53bfee478bf689f8e012fe7988bf755e3d7c5152947abc149bc20189;\nallow if true;\n",
           "revocation_ids": [
             "3771cefe71beb21ead35a59c8116ee82627a5717c0295f35980662abccb159fe1b37848cb1818e548656bd4fd882d0094a2daab631c76b2b72e3a093914bfe04",
-            "45133b90f228a81fe4d3042a79f6c6b7608e656e903d6b1f4db32cd774b09b8315af360879a5f210ad7be37ff55e3eb34f237bcc9711407b6329ac6018bfb400",
-            "179f054f3c572646aba5013159ae192ac42f5666dbdd984129955f4652b6829e59f54aa251e451f96329d42a2524ce569c3e1ec52e708b642dd8994af51dd703",
-            "edab54789d6656936fcd28200b9c61643434842d531f09f209fad555e11ff53174db174dafba126e6de448983a56f78d2042bc5782d71a45799c022fe69fb30d",
-            "6a62306831e9dbe83e7b33db96b758c77dd690930f2d2d87e239b210b1944c5582bf6d7e1bfea8e7f928c27f2fff0e2ee2e0adc41e11e0c3abe8d7b96b9ede07"
+            "6528db2c9a561ada9086268549a600a8a52ff434ea8183812623eec0e9b6c5d3c41ab7868808623021d92294d583afdf92f4354bcdaa1bc50453e1b89afd630d",
+            "5d5679fe69bfe74b7919323515e9ecba9d01422b16be9341b57f88e695b2bb0bd7966b781001d2b9e00ee618fdc239c96e17e32cb379f13f12d6bd7b1b47ad04",
+            "c37bf24c063f0310eccab8864e48dbeffcdd7240b4f8d1e01eba4fc703e6c9082b845bb55543b10f008dc7f4e78540411912ac1f36fa2aa90011dca40f323b09",
+            "3f675d6c364e06405d4868c904e40f3d81c32b083d91586db814d4cb4bf536b4ba209d82f11b4cb6da293b60b20d6122fc3e0e08e80c381dee83edd848211900"
           ]
         }
       }
diff --git a/biscuit-auth/samples/test024_third_party.bc b/biscuit-auth/samples/test024_third_party.bc
index 7bca415c..d2aef528 100644
Binary files a/biscuit-auth/samples/test024_third_party.bc and b/biscuit-auth/samples/test024_third_party.bc differ
diff --git a/biscuit-auth/samples/test026_public_keys_interning.bc b/biscuit-auth/samples/test026_public_keys_interning.bc
index 49e417b2..392d649c 100644
Binary files a/biscuit-auth/samples/test026_public_keys_interning.bc and b/biscuit-auth/samples/test026_public_keys_interning.bc differ
diff --git a/biscuit-auth/src/format/convert.rs b/biscuit-auth/src/format/convert.rs
index 427e5e68..d1e2cef2 100644
--- a/biscuit-auth/src/format/convert.rs
+++ b/biscuit-auth/src/format/convert.rs
@@ -77,6 +77,12 @@ pub fn proto_block_to_token_block(
         ));
     }
 
+    if version != MAX_SCHEMA_VERSION && external_key.is_some() {
+        return Err(error::Format::DeserializationError(
+            "deserialization error: third-party blocks must be v5".to_string(),
+        ));
+    }
+
     for check in input.checks_v2.iter() {
         checks.push(v2::proto_check_to_token_check(check, version)?);
     }
@@ -86,12 +92,12 @@ pub fn proto_block_to_token_block(
 
     let context = input.context.clone();
 
-    let symbols = SymbolTable::from(input.symbols.clone())?;
     let mut public_keys = PublicKeys::new();
-
     for pk in &input.public_keys {
         public_keys.insert_fallible(&PublicKey::from_proto(pk)?)?;
     }
+    let symbols =
+        SymbolTable::from_symbols_and_public_keys(input.symbols.clone(), public_keys.keys.clone())?;
 
     let detected_schema_version = get_schema_version(&facts, &rules, &checks, &scopes);
 
diff --git a/biscuit-auth/src/format/mod.rs b/biscuit-auth/src/format/mod.rs
index 48643d71..90816111 100644
--- a/biscuit-auth/src/format/mod.rs
+++ b/biscuit-auth/src/format/mod.rs
@@ -14,7 +14,6 @@ use super::token::Block;
 use crate::crypto::ExternalSignature;
 use crate::datalog::SymbolTable;
 use crate::token::RootKeyProvider;
-use std::collections::HashMap;
 use std::convert::TryInto;
 
 /// Structures generated from the Protobuf schema
@@ -143,14 +142,7 @@ impl SerializedBiscuit {
     pub(crate) fn extract_blocks(
         &self,
         symbols: &mut SymbolTable,
-    ) -> Result<
-        (
-            schema::Block,
-            Vec<schema::Block>,
-            HashMap<usize, Vec<usize>>,
-        ),
-        error::Token,
-    > {
+    ) -> Result<(schema::Block, Vec<schema::Block>), error::Token> {
         let mut block_external_keys = Vec::new();
 
         let authority = schema::Block::decode(&self.authority.data[..]).map_err(|e| {
@@ -182,34 +174,21 @@ impl SerializedBiscuit {
             })?;
 
             if let Some(external_signature) = &block.external_signature {
-                symbols.public_keys.insert(&external_signature.public_key);
                 block_external_keys.push(Some(external_signature.public_key));
             } else {
                 block_external_keys.push(None);
                 symbols.extend(&SymbolTable::from(deser.symbols.clone())?)?;
-            }
-
-            for pk in &deser.public_keys {
-                symbols
-                    .public_keys
-                    .insert_fallible(&PublicKey::from_proto(pk)?)?;
+                for pk in &deser.public_keys {
+                    symbols
+                        .public_keys
+                        .insert_fallible(&PublicKey::from_proto(pk)?)?;
+                }
             }
 
             blocks.push(deser);
         }
 
-        let mut public_key_to_block_id: HashMap<usize, Vec<usize>> = HashMap::new();
-        for (index, opt_key) in block_external_keys.into_iter().enumerate() {
-            if let Some(key) = opt_key {
-                if let Some(key_index) = symbols.public_keys.get(&key) {
-                    public_key_to_block_id
-                        .entry(key_index as usize)
-                        .or_default()
-                        .push(index);
-                }
-            }
-        }
-        Ok((authority, blocks, public_key_to_block_id))
+        Ok((authority, blocks))
     }
 
     /// serializes the token
diff --git a/biscuit-auth/src/token/authorizer.rs b/biscuit-auth/src/token/authorizer.rs
index 027b6e9c..922beacd 100644
--- a/biscuit-auth/src/token/authorizer.rs
+++ b/biscuit-auth/src/token/authorizer.rs
@@ -5,7 +5,7 @@ use super::builder::{
 };
 use super::builder_ext::{AuthorizerExt, BuilderExt};
 use super::{Biscuit, Block};
-use crate::builder::{CheckKind, Convert};
+use crate::builder::{self, CheckKind, Convert};
 use crate::crypto::PublicKey;
 use crate::datalog::{self, Origin, RunLimits, SymbolTable, TrustedOrigins};
 use crate::error;
@@ -87,16 +87,15 @@ impl Authorizer {
             return Err(error::Logic::AuthorizerNotEmpty.into());
         }
 
-        for (key_id, block_ids) in &token.public_key_to_block_id {
-            let key = token
-                .symbols
-                .public_keys
-                .get_key(*key_id as u64)
-                .ok_or(error::Format::UnknownExternalKey)?;
-            let new_key_id = self.symbols.public_keys.insert(key);
+        for (i, block) in token.container.blocks.iter().enumerate() {
+            if let Some(sig) = block.external_signature.as_ref() {
+                let new_key_id = self.symbols.public_keys.insert(&sig.public_key);
 
-            self.public_key_to_block_id
-                .insert(new_key_id as usize, block_ids.clone());
+                self.public_key_to_block_id
+                    .entry(new_key_id as usize)
+                    .or_default()
+                    .push(i + 1);
+            }
         }
 
         let mut blocks = Vec::new();
@@ -120,7 +119,7 @@ impl Authorizer {
         Ok(())
     }
 
-    /// we need to modify the block loaded from the token, because the authorizer's and th token's symbol table can differ
+    /// we need to modify the block loaded from the token, because the authorizer's and the token's symbol table can differ
     fn load_and_translate_block(
         &mut self,
         block: &mut Block,
@@ -131,14 +130,17 @@ impl Authorizer {
         let block_symbols = if i == 0 || block.external_key.is_none() {
             token_symbols.clone()
         } else {
-            let mut symbols = block.symbols.clone();
-            symbols.public_keys = token_symbols.public_keys.clone();
-            symbols
+            block.symbols.clone()
         };
 
         let mut block_origin = Origin::default();
         block_origin.insert(i);
 
+        for scope in block.scopes.iter_mut() {
+            *scope = builder::Scope::convert_from(scope, &block_symbols)
+                .map(|s| s.convert(&mut self.symbols))?;
+        }
+
         let block_trusted_origins = TrustedOrigins::from_scopes(
             &block.scopes,
             &TrustedOrigins::default(),
diff --git a/biscuit-auth/src/token/mod.rs b/biscuit-auth/src/token/mod.rs
index 2fedac95..fe1b089e 100644
--- a/biscuit-auth/src/token/mod.rs
+++ b/biscuit-auth/src/token/mod.rs
@@ -1,5 +1,4 @@
 //! main structures to interact with Biscuit tokens
-use std::collections::HashMap;
 use std::convert::TryInto;
 use std::fmt::Display;
 
@@ -32,7 +31,7 @@ pub use third_party::*;
 /// minimum supported version of the serialization format
 pub const MIN_SCHEMA_VERSION: u32 = 3;
 /// maximum supported version of the serialization format
-pub const MAX_SCHEMA_VERSION: u32 = 4;
+pub const MAX_SCHEMA_VERSION: u32 = 5;
 
 /// some symbols are predefined and available in every implementation, to avoid
 /// transmitting them with every token
@@ -78,7 +77,6 @@ pub struct Biscuit {
     pub(crate) blocks: Vec<schema::Block>,
     pub(crate) symbols: SymbolTable,
     pub(crate) container: SerializedBiscuit,
-    pub(crate) public_key_to_block_id: HashMap<usize, Vec<usize>>,
 }
 
 impl Biscuit {
@@ -259,7 +257,6 @@ impl Biscuit {
             blocks,
             symbols,
             container,
-            public_key_to_block_id: HashMap::new(),
         })
     }
 
@@ -282,7 +279,7 @@ impl Biscuit {
         container: SerializedBiscuit,
         mut symbols: SymbolTable,
     ) -> Result<Self, error::Token> {
-        let (authority, blocks, public_key_to_block_id) = container.extract_blocks(&mut symbols)?;
+        let (authority, blocks) = container.extract_blocks(&mut symbols)?;
 
         let root_key_id = container.root_key_id;
 
@@ -292,7 +289,6 @@ impl Biscuit {
             blocks,
             symbols,
             container,
-            public_key_to_block_id,
         })
     }
 
@@ -333,23 +329,12 @@ impl Biscuit {
         let authority = self.authority.clone();
         let mut blocks = self.blocks.clone();
         let mut symbols = self.symbols.clone();
-        let mut public_key_to_block_id = self.public_key_to_block_id.clone();
 
         let container = self.container.append(keypair, &block, None)?;
 
         symbols.extend(&block.symbols)?;
         symbols.public_keys.extend(&block.public_keys)?;
 
-        if let Some(index) = block
-            .external_key
-            .as_ref()
-            .and_then(|pk| symbols.public_keys.get(pk))
-        {
-            public_key_to_block_id
-                .entry(index as usize)
-                .or_default()
-                .push(self.block_count() + 1);
-        }
         let deser = schema::Block::decode(
             &container
                 .blocks
@@ -371,7 +356,6 @@ impl Biscuit {
             blocks,
             symbols,
             container,
-            public_key_to_block_id,
         })
     }
 
@@ -443,30 +427,13 @@ impl Biscuit {
             signature,
         };
 
-        let mut symbols = self.symbols.clone();
-        let mut public_key_to_block_id = self.public_key_to_block_id.clone();
+        let symbols = self.symbols.clone();
         let mut blocks = self.blocks.clone();
 
         let container =
             self.container
                 .append_serialized(&next_keypair, payload, Some(external_signature))?;
 
-        let token_block = proto_block_to_token_block(&block, Some(external_key)).unwrap();
-        for key in &token_block.public_keys.keys {
-            symbols.public_keys.insert_fallible(key)?;
-        }
-
-        if let Some(index) = token_block
-            .external_key
-            .as_ref()
-            .and_then(|pk| symbols.public_keys.get(pk))
-        {
-            public_key_to_block_id
-                .entry(index as usize)
-                .or_default()
-                .push(self.block_count());
-        }
-
         blocks.push(block);
 
         Ok(Biscuit {
@@ -475,7 +442,6 @@ impl Biscuit {
             blocks,
             symbols,
             container,
-            public_key_to_block_id,
         })
     }
 
@@ -535,7 +501,7 @@ impl Biscuit {
     }
 
     pub(crate) fn block(&self, index: usize) -> Result<Block, error::Token> {
-        let mut block = if index == 0 {
+        let block = if index == 0 {
             proto_block_to_token_block(
                 &self.authority,
                 self.container
@@ -562,9 +528,6 @@ impl Biscuit {
             .map_err(error::Token::Format)?
         };
 
-        // we have to add the entire list of public keys here because
-        // they are used to validate 3rd party tokens
-        block.symbols.public_keys = self.symbols.public_keys.clone();
         Ok(block)
     }
 }
@@ -645,7 +608,7 @@ fn print_block(symbols: &SymbolTable, block: &Block) -> String {
 pub enum Scope {
     Authority,
     Previous,
-    // index of the public key in the token's list
+    // index of the public key in the symbol table
     PublicKey(u64),
 }
 
diff --git a/biscuit-auth/src/token/third_party.rs b/biscuit-auth/src/token/third_party.rs
index e9aed202..c6e300bf 100644
--- a/biscuit-auth/src/token/third_party.rs
+++ b/biscuit-auth/src/token/third_party.rs
@@ -10,13 +10,10 @@ use crate::{
     KeyPair, PrivateKey,
 };
 
-use super::public_keys::PublicKeys;
-
 /// Third party block request
 #[derive(Debug)]
 pub struct ThirdPartyRequest {
     pub(crate) previous_key: PublicKey,
-    pub(crate) public_keys: PublicKeys,
 }
 
 impl ThirdPartyRequest {
@@ -27,52 +24,21 @@ impl ThirdPartyRequest {
             return Err(error::Token::AppendOnSealed);
         }
 
-        let mut public_keys = PublicKeys::new();
-
-        for pk in &schema::Block::decode(&container.authority.data[..])
-            .map_err(|e| {
-                error::Format::DeserializationError(format!("deserialization error: {:?}", e))
-            })?
-            .public_keys
-        {
-            public_keys.insert(&PublicKey::from_proto(pk)?);
-        }
-        for block in &container.blocks {
-            for pk in &schema::Block::decode(&block.data[..])
-                .map_err(|e| {
-                    error::Format::DeserializationError(format!("deserialization error: {:?}", e))
-                })?
-                .public_keys
-            {
-                public_keys.insert(&PublicKey::from_proto(pk)?);
-            }
-        }
-
         let previous_key = container
             .blocks
             .last()
             .unwrap_or(&container.authority)
             .next_key;
 
-        Ok(ThirdPartyRequest {
-            previous_key,
-            public_keys,
-        })
+        Ok(ThirdPartyRequest { previous_key })
     }
 
     pub fn serialize(&self) -> Result<Vec<u8>, error::Token> {
-        let public_keys = self
-            .public_keys
-            .keys
-            .iter()
-            .map(|key| key.to_proto())
-            .collect();
-
         let previous_key = self.previous_key.to_proto();
 
         let request = schema::ThirdPartyBlockRequest {
             previous_key,
-            public_keys,
+            public_keys: Vec::new(),
         };
         let mut v = Vec::new();
 
@@ -95,16 +61,13 @@ impl ThirdPartyRequest {
 
         let previous_key = PublicKey::from_proto(&data.previous_key)?;
 
-        let mut public_keys = PublicKeys::new();
-
-        for key in data.public_keys {
-            public_keys.insert(&PublicKey::from_proto(&key)?);
+        if !data.public_keys.is_empty() {
+            return Err(error::Token::Format(error::Format::DeserializationError(
+                "public keys were provided in third-party block request".to_owned(),
+            )));
         }
 
-        Ok(ThirdPartyRequest {
-            previous_key,
-            public_keys,
-        })
+        Ok(ThirdPartyRequest { previous_key })
     }
 
     pub fn deserialize_base64<T>(slice: T) -> Result<Self, error::Token>
@@ -121,8 +84,7 @@ impl ThirdPartyRequest {
         private_key: &PrivateKey,
         block_builder: BlockBuilder,
     ) -> Result<ThirdPartyBlock, error::Token> {
-        let mut symbols = SymbolTable::new();
-        symbols.public_keys = self.public_keys.clone();
+        let symbols = SymbolTable::new();
         let mut block = block_builder.build(symbols);
         block.version = super::MAX_SCHEMA_VERSION;
 
diff --git a/biscuit-auth/src/token/unverified.rs b/biscuit-auth/src/token/unverified.rs
index 0cf8c501..28500b3f 100644
--- a/biscuit-auth/src/token/unverified.rs
+++ b/biscuit-auth/src/token/unverified.rs
@@ -1,4 +1,3 @@
-use std::collections::HashMap;
 use std::convert::TryInto;
 
 use super::{default_symbol_table, Biscuit, Block};
@@ -26,7 +25,6 @@ pub struct UnverifiedBiscuit {
     pub(crate) authority: schema::Block,
     pub(crate) blocks: Vec<schema::Block>,
     pub(crate) symbols: SymbolTable,
-    pub(crate) public_key_to_block_id: HashMap<usize, Vec<usize>>,
     container: SerializedBiscuit,
 }
 
@@ -69,7 +67,6 @@ impl UnverifiedBiscuit {
             authority: self.authority,
             blocks: self.blocks,
             symbols: self.symbols,
-            public_key_to_block_id: self.public_key_to_block_id,
             container: self.container,
         })
     }
@@ -100,13 +97,12 @@ impl UnverifiedBiscuit {
     pub fn from_with_symbols(slice: &[u8], mut symbols: SymbolTable) -> Result<Self, error::Token> {
         let container = SerializedBiscuit::deserialize(slice)?;
 
-        let (authority, blocks, public_key_to_block_id) = container.extract_blocks(&mut symbols)?;
+        let (authority, blocks) = container.extract_blocks(&mut symbols)?;
 
         Ok(UnverifiedBiscuit {
             authority,
             blocks,
             symbols,
-            public_key_to_block_id,
             container,
         })
     }
@@ -138,24 +134,12 @@ impl UnverifiedBiscuit {
         let authority = self.authority.clone();
         let mut blocks = self.blocks.clone();
         let mut symbols = self.symbols.clone();
-        let mut public_key_to_block_id = self.public_key_to_block_id.clone();
 
         let container = self.container.append(keypair, &block, None)?;
 
         symbols.extend(&block.symbols)?;
         symbols.public_keys.extend(&block.public_keys)?;
 
-        if let Some(index) = block
-            .external_key
-            .as_ref()
-            .and_then(|pk| symbols.public_keys.get(pk))
-        {
-            public_key_to_block_id
-                .entry(index as usize)
-                .or_default()
-                .push(self.block_count() + 1);
-        }
-
         let deser = schema::Block::decode(
             &container
                 .blocks
@@ -175,7 +159,6 @@ impl UnverifiedBiscuit {
             authority,
             blocks,
             symbols,
-            public_key_to_block_id,
             container,
         })
     }
@@ -340,7 +323,6 @@ impl UnverifiedBiscuit {
         };
 
         let mut symbols = self.symbols.clone();
-        let mut public_key_to_block_id = self.public_key_to_block_id.clone();
         let mut blocks = self.blocks.clone();
 
         let container =
@@ -352,17 +334,6 @@ impl UnverifiedBiscuit {
             symbols.public_keys.insert_fallible(key)?;
         }
 
-        if let Some(index) = token_block
-            .external_key
-            .as_ref()
-            .and_then(|pk| symbols.public_keys.get(pk))
-        {
-            public_key_to_block_id
-                .entry(index as usize)
-                .or_default()
-                .push(self.block_count());
-        }
-
         blocks.push(block);
 
         Ok(UnverifiedBiscuit {
@@ -370,7 +341,6 @@ impl UnverifiedBiscuit {
             blocks,
             symbols,
             container,
-            public_key_to_block_id,
         })
     }