Operations and Examples

Booleans

Native homomorphic booleans support common boolean operations.

The list of supported operations is:

name	symbol	type
BitAnd	&	Binary
BitOr	|	Binary
BitXor	^	Binary
Neg	!	Unary

ShortInt

Native small homomorphic integer types (e.g., FheUint3 or FheUint4) allow to easily compute various operations. In general, computing over encrypted data is as easy as computing over clear data, since the same operation symbol is used. For instance, the addition between two ciphertexts is done using the symbol + between two FheUint. Similarly, many operations can be computed between a clear value (i.e. a scalar) and a ciphertext.

In Rust native types, any operation is modular. In Rust, u8, computations are done modulus 2^8. The similar idea is applied for FheUintX, where operations are done modulus 2^X. For instance, in the type FheUint3, operations are done modulus 8.

Arithmetic operations

Small homomorphic integer types support all common arithmetic operations, meaning +, -, x, /, mod.

The division operation implements a subtlety: since data is encrypted, it might be possible to compute a division by 0. In this case, the division is tweaked so that dividing by 0 returns 0.

The list of supported operations is:

name	symbol	type
Add	+	Binary
Sub	-	Binary
Mul	*	Binary
Div	/	Binary
Rem	%	Binary
Neg	!	Unary

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint3};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint3().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 7;
    let clear_b = 3;
    let clear_c = 2;

    let mut a = FheUint3::try_encrypt(clear_a, &keys)?;
    let mut b = FheUint3::try_encrypt(clear_b, &keys)?;
    let mut c = FheUint3::try_encrypt(clear_c, &keys)?;


    a = a * &b;  // Clear equivalent computations: 7 * 3 mod 8 = 5
    b = &b + &c; // Clear equivalent computations: 3 + 2 mod 8 = 5
    b = b - 5;   // Clear equivalent computations: 5 - 5 mod 8 = 0
    
    let dec_a = a.decrypt(&keys);
    let dec_b = b.decrypt(&keys);
    
    // We homomorphically swapped values using bitwise operations
    assert_eq!(dec_a, (clear_a * clear_b) % 8);
    assert_eq!(dec_b, ((clear_b + clear_c) - 5) % 8);

    Ok(())
}

Bitwise operations

Small homomorphic integer types support some bitwise operations.

The list of supported operations is:

name	symbol	type
BitAnd	&	Binary
BitOr	|	Binary
BitXor	^	Binary
Shr	>>	Binary
Shl	<<	Binary

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint3};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint3().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 7;
    let clear_b = 3;
    
    let mut a = FheUint3::try_encrypt(clear_a, &keys)?;
    let mut b = FheUint3::try_encrypt(clear_b, &keys)?;
    
    a = a ^ &b;
    b = b ^ &a;
    a = a ^ &b;
    
    let dec_a = a.decrypt(&keys);
    let dec_b = b.decrypt(&keys);
    
    // We homomorphically swapped values using bitwise operations
    assert_eq!(dec_a, clear_b);
    assert_eq!(dec_b, clear_a);

    Ok(())
}

Comparisons

Small homomorphic integer types support comparison operations.

However, due to some Rust limitations, this is not possible to overload the comparison symbols because of the inner definition of the operations. To be precise, Rust expects to have a boolean as output, whereas a ciphertext encrypted the result is returned when using homomorphic types.

So instead of using symbols for the comparisons, you will need to use the different methods. These methods follow the same naming that the 2 standard Rust trait

• PartialOrd

• PartialEq

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint3};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint3().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 7;
    let clear_b = 3;
    
    let mut a = FheUint3::try_encrypt(clear_a, &keys)?;
    let mut b = FheUint3::try_encrypt(clear_b, &keys)?;
    
    assert_eq!(a.gt(&b).decrypt(&keys) != 0, true);
    assert_eq!(b.le(&a).decrypt(&keys) != 0, true);

    Ok(())
}

Univariate function evaluations

Shortints type also support the computation of univariate functions, which deep down uses TFHE's programmable bootstrapping.

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint4};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint4().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);

    let pow_5 = |value: u64| {
        value.pow(5) % FheUint4::MODULUS as u64
    };

    let clear_a = 12;
    let a = FheUint4::try_encrypt(12, &keys)?;

    let c = a.map(pow_5);
    let decrypted = c.decrypt(&keys);
    assert_eq!(decrypted, pow_5(clear_a) as u8);

    Ok(())
}

Bivariate function evaluations

Using the shortint types offers the possibility to evaluate bivariate functions, i.e., functions that takes two ciphertexts as input.

In what follows, a simple code example:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint2};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint2().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 1;
    let clear_b = 3;
    let a = FheUint2::try_encrypt(clear_a, &keys)?;
    let b = FheUint2::try_encrypt(clear_b, &keys)?;

    
    let c = a.bivariate_function(&b, std::cmp::max);
    let decrypted = c.decrypt(&keys);
    assert_eq!(decrypted, std::cmp::max(clear_a, clear_b) as u8);

    Ok(())
}

Integer.

In the same vein, native homomorphic types supports modular operations. At the moment, integers are more limited than shortint, but operations will be added soon.

Arithmetic operations

Homomorphic integer types support arithmetic operations.

The list of supported operations is:

name	symbol	type
Add	+	Binary
Sub	-	Binary
Mul	*	Binary
Neg	!	Unary

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint8};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint8().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 15_i64;
    let clear_b = 27_i64;
    let clear_c = 43_i64;

    let mut a = FheUint8::try_encrypt(clear_a, &keys)?;
    let mut b = FheUint8::try_encrypt(clear_b, &keys)?;
    let mut c = FheUint8::try_encrypt(clear_c, &keys)?;


    a = a * &b;  // Clear equivalent computations: 15 * 27 mod 256 = 149
    b = &b + &c; // Clear equivalent computations: 27 + 43 mod 256 = 70
    b = b - 76u8;   // Clear equivalent computations: 70 - 76 mod 256 = 250
    
    let dec_a: u8 = a.decrypt(&keys);
    let dec_b: u8 = b.decrypt(&keys);
    
    assert_eq!(dec_a, ((clear_a * clear_b) % 256_i64) as u8);
    assert_eq!(dec_b, (((clear_b  + clear_c) - 76_i64) % 256_i64) as u8);

    Ok(())
}

Bitwise operations

Homomorphic integer types support some bitwise operations.

The list of supported operations is:

name	symbol	type
BitAnd	&	Binary
BitOr	|	Binary
BitXor	^	Binary
Shr	>>	Binary
Shl	<<	Binary

A simple example on how to use these operations:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint8};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint8().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);
    
    let clear_a = 164;
    let clear_b = 212;

    let mut a = FheUint8::try_encrypt(clear_a, &keys)?;
    let mut b = FheUint8::try_encrypt(clear_b, &keys)?;


    a = a ^ &b;
    b = b ^ &a;
    a = a ^ &b;

    let dec_a: u8 = a.decrypt(&keys);
    let dec_b: u8 = b.decrypt(&keys);

    // We homomorphically swapped values using bitwise operations
    assert_eq!(dec_a, clear_b);
    assert_eq!(dec_b, clear_a);

    Ok(())
}

Univariate function evaluations

As for shortints, homomorphic integers support the evaluation of univariate functions.

Here, an example on how to use this operation:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint16};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint16().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);

    let hamming_weight = |value: u64| {
        value.count_ones() as u64
    };

    let clear_a = 157u64;
    let a = FheUint16::try_encrypt(clear_a, &keys)?;

    let c = a.map(hamming_weight);
    let decrypted: u16 = c.decrypt(&keys);
    assert_eq!(decrypted, hamming_weight(clear_a) as u16);

    Ok(())
}

Bivariate function evaluations

Bivariate function evaluations are now supported by integers.

If the precision is too large, this operation might fail due to an out of memory error

An example of this operation:

use concrete::prelude::*;
use concrete::{generate_keys, set_server_key, ConfigBuilder, FheUint8};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let config = ConfigBuilder::all_disabled().enable_default_uint8().build();
    let (keys, server_keys) = generate_keys(config);
    set_server_key(server_keys);

    let some_func = |x: u64, y: u64| {
        if x.count_ones() > y.count_zeros() {
            x.reverse_bits()
        }
        else {
            y.reverse_bits()
        }
    };

    let clear_a = 157;
    let clear_b = 112;

    let a = FheUint8::try_encrypt(clear_a, &keys)?;
    let b = FheUint8::try_encrypt(clear_b, &keys)?;

    let c = a.bivariate_function(&b, some_func);
    let decrypted: u8 = c.decrypt(&keys);
    assert_eq!(decrypted, some_func(clear_a, clear_b) as u8);

    Ok(())
}