diff --git a/Changelog.md b/Changelog.md
index 0977ded..330667b 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,14 @@
+# Version 1.2.0, 2020-06, Arithmetic circuits
+
+Interface definition:
+- Added constraint_type to support for both R1CS and arithmetic circuits.
+- *(breaking)* Position of the field `ConstraintSystem.info` (unused afaik.).
+
+Rust:
+- *(breaking)* New field `ConstraintSystemOwned.constraint_type`
+- A function to validate that a constraint system is indeed an arithmetic circuit (`validate_constraint_type`).
+
+
 # Version 1.1.0, 2020-06, Simplifications
 
 Interface definition:
diff --git a/examples/example.json b/examples/example.json
index 552be0d..f3b1f25 100644
--- a/examples/example.json
+++ b/examples/example.json
@@ -109,7 +109,8 @@
             ]
           }
         }
-      ]
+      ],
+      "constraint_type": "R1CS"
     }
   ],
   "witnesses": [
diff --git a/rust/src/examples.rs b/rust/src/examples.rs
index 5e5ead3..1c481a5 100644
--- a/rust/src/examples.rs
+++ b/rust/src/examples.rs
@@ -3,7 +3,7 @@ use std::io;
 use std::mem::size_of;
 use owned::circuit::CircuitOwned;
 use owned::variables::VariablesOwned;
-use zkinterface_generated::zkinterface::{BilinearConstraint, BilinearConstraintArgs, Message, ConstraintSystem, ConstraintSystemArgs, Root, RootArgs, Variables, VariablesArgs, Witness, WitnessArgs};
+use zkinterface_generated::zkinterface::{BilinearConstraint, BilinearConstraintArgs, Message, ConstraintSystem, ConstraintSystemArgs, Root, RootArgs, Variables, VariablesArgs, Witness, WitnessArgs, ConstraintType};
 
 
 pub fn example_circuit() -> CircuitOwned {
@@ -58,6 +58,7 @@ pub fn write_example_constraints<W: io::Write>(mut writer: W) -> io::Result<()>
     let constraints_built = builder.create_vector(&constraints_built);
     let r1cs = ConstraintSystem::create(&mut builder, &ConstraintSystemArgs {
         constraints: Some(constraints_built),
+        constraint_type: ConstraintType::R1CS,
         info: None,
     });
 
diff --git a/rust/src/owned/constraints.rs b/rust/src/owned/constraints.rs
index 7163be6..1d5ec0d 100644
--- a/rust/src/owned/constraints.rs
+++ b/rust/src/owned/constraints.rs
@@ -1,10 +1,12 @@
 use owned::variables::VariablesOwned;
 use serde::{Deserialize, Serialize};
-use zkinterface_generated::zkinterface::ConstraintSystem;
+use zkinterface_generated::zkinterface::{ConstraintSystem, ConstraintType};
 
 #[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
 pub struct ConstraintSystemOwned {
     pub constraints: Vec<BilinearConstraintOwned>,
+
+    pub constraint_type: ConstraintTypeOwned,
 }
 
 #[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
@@ -19,6 +21,7 @@ impl<'a> From<ConstraintSystem<'a>> for ConstraintSystemOwned {
     fn from(constraints_ref: ConstraintSystem) -> ConstraintSystemOwned {
         let mut owned = ConstraintSystemOwned {
             constraints: vec![],
+            constraint_type: constraints_ref.constraint_type().into(),
         };
 
         let cons_ref = constraints_ref.constraints().unwrap();
@@ -34,3 +37,30 @@ impl<'a> From<ConstraintSystem<'a>> for ConstraintSystemOwned {
         owned
     }
 }
+
+
+#[allow(non_camel_case_types)]
+#[repr(i8)]
+#[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
+pub enum ConstraintTypeOwned {
+    R1CS = 0,
+    arithmetic = 1,
+}
+
+impl From<ConstraintType> for ConstraintTypeOwned {
+    fn from(ct: ConstraintType) -> Self {
+        match ct {
+            ConstraintType::R1CS => ConstraintTypeOwned::R1CS,
+            ConstraintType::arithmetic => ConstraintTypeOwned::arithmetic,
+        }
+    }
+}
+
+impl Into<ConstraintType> for ConstraintTypeOwned {
+    fn into(self) -> ConstraintType {
+        match self {
+            ConstraintTypeOwned::R1CS => ConstraintType::R1CS,
+            ConstraintTypeOwned::arithmetic => ConstraintType::arithmetic,
+        }
+    }
+}
\ No newline at end of file
diff --git a/rust/src/reading.rs b/rust/src/reading.rs
index 10a8f69..77358f0 100644
--- a/rust/src/reading.rs
+++ b/rust/src/reading.rs
@@ -9,6 +9,7 @@ use std::path::Path;
 use zkinterface_generated::zkinterface::{
     BilinearConstraint,
     Circuit,
+    ConstraintType,
     get_size_prefixed_root_as_root,
     Root,
     Variables,
@@ -299,6 +300,36 @@ impl Messages {
             constraints: None,
         }
     }
+
+    pub fn validate_constraint_type(&self) -> Result<(), String> {
+        for message in self.into_iter() {
+            match message.message_as_constraint_system() {
+                None => continue,
+                Some(cs) => {
+                    if cs.constraint_type() == ConstraintType::arithmetic {
+                        let constraints = cs.constraints().unwrap();
+                        for i in 0..constraints.len() {
+                            let constraint = constraints.get(i);
+                            let n_a = constraint.linear_combination_a().unwrap().variable_ids().unwrap().len();
+                            let n_b = constraint.linear_combination_b().unwrap().variable_ids().unwrap().len();
+                            let n_c = constraint.linear_combination_c().unwrap().variable_ids().unwrap().len();
+
+                            let is_pure_multiplication =
+                                n_a == 1 && n_b == 1 && n_c == 1;
+
+                            let is_pure_linear =
+                                n_a == 0 && n_b == 0;
+
+                            if !(is_pure_multiplication || is_pure_linear) {
+                                return Err("The circuit should be fan-in 2 but constraints are not in the correct format.".to_string());
+                            }
+                        }
+                    }
+                }
+            };
+        }
+        Ok(())
+    }
 }
 
 pub type Term<'a> = Variable<'a>;
diff --git a/rust/src/zkinterface_generated.rs b/rust/src/zkinterface_generated.rs
index e24c071..ac1511b 100644
--- a/rust/src/zkinterface_generated.rs
+++ b/rust/src/zkinterface_generated.rs
@@ -87,6 +87,66 @@ pub fn enum_name_message(e: Message) -> &'static str {
 }
 
 pub struct MessageUnionTableOffset {}
+#[allow(non_camel_case_types)]
+#[repr(i8)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+pub enum ConstraintType {
+  R1CS = 0,
+  arithmetic = 1,
+
+}
+
+pub const ENUM_MIN_CONSTRAINT_TYPE: i8 = 0;
+pub const ENUM_MAX_CONSTRAINT_TYPE: i8 = 1;
+
+impl<'a> flatbuffers::Follow<'a> for ConstraintType {
+  type Inner = Self;
+  #[inline]
+  fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
+    flatbuffers::read_scalar_at::<Self>(buf, loc)
+  }
+}
+
+impl flatbuffers::EndianScalar for ConstraintType {
+  #[inline]
+  fn to_little_endian(self) -> Self {
+    let n = i8::to_le(self as i8);
+    let p = &n as *const i8 as *const ConstraintType;
+    unsafe { *p }
+  }
+  #[inline]
+  fn from_little_endian(self) -> Self {
+    let n = i8::from_le(self as i8);
+    let p = &n as *const i8 as *const ConstraintType;
+    unsafe { *p }
+  }
+}
+
+impl flatbuffers::Push for ConstraintType {
+    type Output = ConstraintType;
+    #[inline]
+    fn push(&self, dst: &mut [u8], _rest: &[u8]) {
+        flatbuffers::emplace_scalar::<ConstraintType>(dst, *self);
+    }
+}
+
+#[allow(non_camel_case_types)]
+pub const ENUM_VALUES_CONSTRAINT_TYPE:[ConstraintType; 2] = [
+  ConstraintType::R1CS,
+  ConstraintType::arithmetic
+];
+
+#[allow(non_camel_case_types)]
+pub const ENUM_NAMES_CONSTRAINT_TYPE:[&'static str; 2] = [
+    "R1CS",
+    "arithmetic"
+];
+
+pub fn enum_name_constraint_type(e: ConstraintType) -> &'static str {
+  let index = e as i8;
+  ENUM_NAMES_CONSTRAINT_TYPE[index as usize]
+}
+
 pub enum CircuitOffset {}
 #[derive(Copy, Clone, Debug, PartialEq)]
 
@@ -253,16 +313,25 @@ impl<'a> ConstraintSystem<'a> {
       let mut builder = ConstraintSystemBuilder::new(_fbb);
       if let Some(x) = args.info { builder.add_info(x); }
       if let Some(x) = args.constraints { builder.add_constraints(x); }
+      builder.add_constraint_type(args.constraint_type);
       builder.finish()
     }
 
     pub const VT_CONSTRAINTS: flatbuffers::VOffsetT = 4;
-    pub const VT_INFO: flatbuffers::VOffsetT = 6;
+    pub const VT_CONSTRAINT_TYPE: flatbuffers::VOffsetT = 6;
+    pub const VT_INFO: flatbuffers::VOffsetT = 8;
 
   #[inline]
   pub fn constraints(&self) -> Option<flatbuffers::Vector<'a, flatbuffers::ForwardsUOffset<BilinearConstraint<'a>>>> {
     self._tab.get::<flatbuffers::ForwardsUOffset<flatbuffers::Vector<flatbuffers::ForwardsUOffset<BilinearConstraint<'a>>>>>(ConstraintSystem::VT_CONSTRAINTS, None)
   }
+  /// Whether this is an R1CS or fan-in-2 arithmetic circuit.
+  /// A special case is a boolean circuit with XOR and AND gates,
+  /// then constraint_type == arithmetic and circuit.field_maximum == 1.
+  #[inline]
+  pub fn constraint_type(&self) -> ConstraintType {
+    self._tab.get::<ConstraintType>(ConstraintSystem::VT_CONSTRAINT_TYPE, Some(ConstraintType::R1CS)).unwrap()
+  }
   /// Optional: Any complementary info that may be useful.
   ///
   /// Example: human-readable descriptions.
@@ -275,6 +344,7 @@ impl<'a> ConstraintSystem<'a> {
 
 pub struct ConstraintSystemArgs<'a> {
     pub constraints: Option<flatbuffers::WIPOffset<flatbuffers::Vector<'a , flatbuffers::ForwardsUOffset<BilinearConstraint<'a >>>>>,
+    pub constraint_type: ConstraintType,
     pub info: Option<flatbuffers::WIPOffset<flatbuffers::Vector<'a , flatbuffers::ForwardsUOffset<KeyValue<'a >>>>>,
 }
 impl<'a> Default for ConstraintSystemArgs<'a> {
@@ -282,6 +352,7 @@ impl<'a> Default for ConstraintSystemArgs<'a> {
     fn default() -> Self {
         ConstraintSystemArgs {
             constraints: None,
+            constraint_type: ConstraintType::R1CS,
             info: None,
         }
     }
@@ -296,6 +367,10 @@ impl<'a: 'b, 'b> ConstraintSystemBuilder<'a, 'b> {
     self.fbb_.push_slot_always::<flatbuffers::WIPOffset<_>>(ConstraintSystem::VT_CONSTRAINTS, constraints);
   }
   #[inline]
+  pub fn add_constraint_type(&mut self, constraint_type: ConstraintType) {
+    self.fbb_.push_slot::<ConstraintType>(ConstraintSystem::VT_CONSTRAINT_TYPE, constraint_type, ConstraintType::R1CS);
+  }
+  #[inline]
   pub fn add_info(&mut self, info: flatbuffers::WIPOffset<flatbuffers::Vector<'b , flatbuffers::ForwardsUOffset<KeyValue<'b >>>>) {
     self.fbb_.push_slot_always::<flatbuffers::WIPOffset<_>>(ConstraintSystem::VT_INFO, info);
   }
diff --git a/zkinterface.fbs b/zkinterface.fbs
index 1aef8f3..e33289c 100644
--- a/zkinterface.fbs
+++ b/zkinterface.fbs
@@ -44,12 +44,20 @@ table Circuit {
     configuration           :[KeyValue];
 }
 
+// A circuit can be R1CS or arithmetic (fan-in 2 multiplications).
+enum ConstraintType : byte { R1CS = 0, arithmetic = 1 }
+
 /// ConstraintSystem represents constraints to be added to the constraint system.
 ///
 /// Multiple such messages are equivalent to the concatenation of `constraints` arrays.
 table ConstraintSystem {
     constraints             :[BilinearConstraint];
 
+    /// Whether this is an R1CS or fan-in-2 arithmetic circuit.
+    /// A special case is a boolean circuit with XOR and AND gates,
+    /// then constraint_type == arithmetic and circuit.field_maximum == 1.
+    constraint_type            :ConstraintType;
+
     /// Optional: Any complementary info that may be useful.
     ///
     /// Example: human-readable descriptions.