diff --git a/Sources/CryptoBoringWrapper/Util/ArbitraryPrecisionInteger.swift b/Sources/CryptoBoringWrapper/Util/ArbitraryPrecisionInteger.swift
index 6b812816..b87efca8 100644
--- a/Sources/CryptoBoringWrapper/Util/ArbitraryPrecisionInteger.swift
+++ b/Sources/CryptoBoringWrapper/Util/ArbitraryPrecisionInteger.swift
@@ -386,6 +386,119 @@ extension ArbitraryPrecisionInteger: Numeric {
     }
 }
 
+// MARK: - Modular arithmetic
+
+extension ArbitraryPrecisionInteger {
+    @usableFromInline
+    package func modulo(_ mod: ArbitraryPrecisionInteger, nonNegative: Bool = false) throws -> ArbitraryPrecisionInteger {
+        var result = ArbitraryPrecisionInteger()
+
+        let rc = result.withUnsafeMutableBignumPointer { resultPtr in
+            self.withUnsafeBignumPointer { selfPtr in
+                mod.withUnsafeBignumPointer { modPtr in
+                    ArbitraryPrecisionInteger.withUnsafeBN_CTX { bnCtx in
+                        if nonNegative {
+                            CCryptoBoringSSL_BN_nnmod(resultPtr, selfPtr, modPtr, bnCtx)
+                        } else {
+                            CCryptoBoringSSLShims_BN_mod(resultPtr, selfPtr, modPtr, bnCtx)
+                        }
+                    }
+                }
+            }
+        }
+        guard rc == 1 else { throw CryptoBoringWrapperError.internalBoringSSLError() }
+
+        return result
+    }
+
+    @usableFromInline
+    package func inverse(modulo mod: ArbitraryPrecisionInteger) throws -> ArbitraryPrecisionInteger {
+        var result = ArbitraryPrecisionInteger()
+
+        let rc = result.withUnsafeMutableBignumPointer { resultPtr in
+            self.withUnsafeBignumPointer { selfPtr in
+                mod.withUnsafeBignumPointer { modPtr in
+                    ArbitraryPrecisionInteger.withUnsafeBN_CTX { bnCtx in
+                        CCryptoBoringSSL_BN_mod_inverse(resultPtr, selfPtr, modPtr, bnCtx)
+                    }
+                }
+            }
+        }
+        guard rc != nil else { throw CryptoBoringWrapperError.internalBoringSSLError() }
+
+        return result
+    }
+
+
+    @usableFromInline
+    package static func inverse(lhs: ArbitraryPrecisionInteger, modulo mod: ArbitraryPrecisionInteger) throws -> ArbitraryPrecisionInteger {
+        try ArbitraryPrecisionInteger(lhs).inverse(modulo: mod)
+    }
+
+    @usableFromInline
+    package func add(_ rhs: ArbitraryPrecisionInteger, modulo modulus: ArbitraryPrecisionInteger? = nil) throws -> ArbitraryPrecisionInteger {
+        guard let modulus else { return self + rhs }
+        var result = ArbitraryPrecisionInteger()
+
+        let rc = result.withUnsafeMutableBignumPointer { resultPtr in
+            self.withUnsafeBignumPointer { selfPtr in
+                rhs.withUnsafeBignumPointer { rhsPtr in
+                    modulus.withUnsafeBignumPointer { modulusPtr in
+                        ArbitraryPrecisionInteger.withUnsafeBN_CTX { bnCtx in
+                            return CCryptoBoringSSL_BN_mod_add(resultPtr, selfPtr, rhsPtr, modulusPtr, bnCtx)
+                        }
+                    }
+                }
+            }
+        }
+        guard rc == 1 else { throw CryptoBoringWrapperError.internalBoringSSLError() }
+
+        return result
+    }
+
+    @usableFromInline
+    package func sub(_ rhs: ArbitraryPrecisionInteger, modulo modulus: ArbitraryPrecisionInteger? = nil) throws -> ArbitraryPrecisionInteger {
+        guard let modulus else { return self - rhs }
+        var result = ArbitraryPrecisionInteger()
+
+        let rc = result.withUnsafeMutableBignumPointer { resultPtr in
+            self.withUnsafeBignumPointer { selfPtr in
+                rhs.withUnsafeBignumPointer { rhsPtr in
+                    modulus.withUnsafeBignumPointer { modulusPtr in
+                        ArbitraryPrecisionInteger.withUnsafeBN_CTX { bnCtx in
+                            CCryptoBoringSSL_BN_mod_sub(resultPtr, selfPtr, rhsPtr, modulusPtr, bnCtx)
+                        }
+                    }
+                }
+            }
+        }
+        guard rc == 1 else { throw CryptoBoringWrapperError.internalBoringSSLError() }
+
+        return result
+    }
+
+    @usableFromInline
+    package func mul(_ rhs: ArbitraryPrecisionInteger, modulo modulus: ArbitraryPrecisionInteger? = nil) throws -> ArbitraryPrecisionInteger {
+        guard let modulus else { return self * rhs }
+        var result = ArbitraryPrecisionInteger()
+
+        let rc = result.withUnsafeMutableBignumPointer { resultPtr in
+            self.withUnsafeBignumPointer { selfPtr in
+                rhs.withUnsafeBignumPointer { rhsPtr in
+                    modulus.withUnsafeBignumPointer { modulusPtr in
+                        ArbitraryPrecisionInteger.withUnsafeBN_CTX { bnCtx in
+                            return CCryptoBoringSSL_BN_mod_mul(resultPtr, selfPtr, rhsPtr, modulusPtr, bnCtx)
+                        }
+                    }
+                }
+            }
+        }
+        guard rc == 1 else { throw CryptoBoringWrapperError.internalBoringSSLError() }
+
+        return result
+    }
+}
+
 // MARK: - SignedNumeric
 
 extension ArbitraryPrecisionInteger: SignedNumeric {
diff --git a/Tests/CryptoBoringWrapperTests/ArbitraryPrecisionIntegerTests.swift b/Tests/CryptoBoringWrapperTests/ArbitraryPrecisionIntegerTests.swift
index 488ad30c..5cd23a09 100644
--- a/Tests/CryptoBoringWrapperTests/ArbitraryPrecisionIntegerTests.swift
+++ b/Tests/CryptoBoringWrapperTests/ArbitraryPrecisionIntegerTests.swift
@@ -167,5 +167,123 @@ final class ArbitraryPrecisionIntegerTests: XCTestCase {
             XCTAssertEqual(try ArbitraryPrecisionInteger(bytes: bytes), integer)
         }
     }
+
+    func testMoudlo() throws {
+        typealias I = ArbitraryPrecisionInteger
+        typealias Vector = (input: I, mod: I, expectedResult: (standard: I, nonNegative: I))
+        for vector: Vector in [
+            (input: 0, mod: 2, expectedResult: (standard: 0, nonNegative: 0)),
+            (input: 1, mod: 2, expectedResult: (standard: 1, nonNegative: 1)),
+            (input: 2, mod: 2, expectedResult: (standard: 0, nonNegative: 0)),
+            (input: 3, mod: 2, expectedResult: (standard: 1, nonNegative: 1)),
+            (input: 4, mod: 2, expectedResult: (standard: 0, nonNegative: 0)),
+            (input: 5, mod: 2, expectedResult: (standard: 1, nonNegative: 1)),
+            (input: 7, mod: 5, expectedResult: (standard: 2, nonNegative: 2)),
+            (input: 7, mod: -5, expectedResult: (standard: 2, nonNegative: 2)),
+            (input: -7, mod: 5, expectedResult: (standard: -2, nonNegative: 3)),
+            (input: -7, mod: -5, expectedResult: (standard: -2, nonNegative: 3)),
+        ] {
+            XCTAssertEqual(
+                try vector.input.modulo(vector.mod, nonNegative: false),
+                vector.expectedResult.standard,
+                "\(vector.input) (mod \(vector.mod))"
+            )
+            XCTAssertEqual(
+                try vector.input.modulo(vector.mod, nonNegative: true),
+                vector.expectedResult.nonNegative,
+                "\(vector.input) (nnmod \(vector.mod))"
+            )
+        }
+    }
+
+    func testModularInverse() throws {
+        typealias I = ArbitraryPrecisionInteger
+        enum O { case ok(I), throwsError }
+        typealias Vector = (a: I, mod: I, expectedResult: O)
+        for vector: Vector in [
+            (a: 3, mod: 7, expectedResult: .ok(5)),
+            (a: 10, mod: 17, expectedResult: .ok(12)),
+            (a: 7, mod: 26, expectedResult: .ok(15)),
+            (a: 7, mod: 7, expectedResult: .throwsError),
+        ] {
+            switch vector.expectedResult {
+            case .ok(let expectedValue):
+                XCTAssertEqual(try vector.a.inverse(modulo: vector.mod), expectedValue, "inverse(\(vector.a), modulo: \(vector.mod))")
+            case .throwsError:
+                XCTAssertThrowsError(try vector.a.inverse(modulo: vector.mod), "inverse(\(vector.a), modulo: \(vector.mod)")
+            }
+        }
+    }
+
+    func testModularAddition() throws {
+        typealias I = ArbitraryPrecisionInteger
+        enum O { case ok(I), throwsError }
+        typealias Vector = (a: I, b: I, mod: I, expectedResult: O)
+        for vector: Vector in [
+            (a: 0, b: 0, mod: 0, expectedResult: .throwsError),
+            (a: 0, b: 0, mod: 2, expectedResult: .ok(0)),
+            (a: 1, b: 0, mod: 2, expectedResult: .ok(1)),
+            (a: 0, b: 1, mod: 2, expectedResult: .ok(1)),
+            (a: 1, b: 1, mod: 2, expectedResult: .ok(0)),
+            (a: 4, b: 3, mod: 5, expectedResult: .ok(2)),
+            (a: 4, b: 3, mod: -5, expectedResult: .ok(2)),
+            (a: -4, b: -3, mod: 5, expectedResult: .ok(3)),
+        ] {
+            switch vector.expectedResult {
+            case .ok(let expectedValue):
+                XCTAssertEqual(try vector.a.add(vector.b, modulo: vector.mod), expectedValue, "\(vector.a) + \(vector.b) (mod \(vector.mod))")
+            case .throwsError:
+                XCTAssertThrowsError(try vector.a.add(vector.b, modulo: vector.mod), "\(vector.a) + \(vector.b) (mod \(vector.mod))")
+            }
+        }
+    }
+
+    func testModularSubtraction() throws {
+        typealias I = ArbitraryPrecisionInteger
+        enum O { case ok(I), throwsError }
+        typealias Vector = (a: I, b: I, mod: I, expectedResult: O)
+        for vector: Vector in [
+            (a: 0, b: 0, mod: 0, expectedResult: .throwsError),
+            (a: 0, b: 0, mod: 2, expectedResult: .ok(0)),
+            (a: 1, b: 0, mod: 2, expectedResult: .ok(1)),
+            (a: 0, b: 1, mod: 2, expectedResult: .ok(1)),
+            (a: 1, b: 1, mod: 2, expectedResult: .ok(0)),
+            (a: 4, b: 3, mod: 5, expectedResult: .ok(1)),
+            (a: 3, b: 4, mod: 5, expectedResult: .ok(4)),
+            (a: 3, b: 4, mod: -5, expectedResult: .ok(4)),
+            (a: -3, b: 4, mod: 5, expectedResult: .ok(3)),
+            (a: 3, b: -4, mod: 5, expectedResult: .ok(2)),
+        ] {
+            switch vector.expectedResult {
+            case .ok(let expectedValue):
+                XCTAssertEqual(try vector.a.sub(vector.b, modulo: vector.mod), expectedValue, "\(vector.a) - \(vector.b) (mod \(vector.mod))")
+            case .throwsError:
+                XCTAssertThrowsError(try vector.a.sub(vector.b, modulo: vector.mod), "\(vector.a) - \(vector.b) (mod \(vector.mod))")
+            }
+        }
+    }
+
+    func testModularMultiplication() throws {
+        typealias I = ArbitraryPrecisionInteger
+        enum O { case ok(I), throwsError }
+        typealias Vector = (a: I, b: I, mod: I, expectedResult: O)
+        for vector: Vector in [
+            (a: 0, b: 0, mod: 0, expectedResult: .throwsError),
+            (a: 0, b: 0, mod: 2, expectedResult: .ok(0)),
+            (a: 1, b: 0, mod: 2, expectedResult: .ok(0)),
+            (a: 0, b: 1, mod: 2, expectedResult: .ok(0)),
+            (a: 1, b: 1, mod: 2, expectedResult: .ok(1)),
+            (a: 4, b: 3, mod: 5, expectedResult: .ok(2)),
+            (a: 4, b: 3, mod: -5, expectedResult: .ok(2)),
+            (a: -4, b: -3, mod: 5, expectedResult: .ok(2)),
+        ] {
+            switch vector.expectedResult {
+            case .ok(let expectedValue):
+                XCTAssertEqual(try vector.a.mul(vector.b, modulo: vector.mod), expectedValue, "\(vector.a) × \(vector.b) (mod \(vector.mod))")
+            case .throwsError:
+                XCTAssertThrowsError(try vector.a.mul(vector.b, modulo: vector.mod), "\(vector.a) × \(vector.b) (mod \(vector.mod))")
+            }
+        }
+    }
 }
 #endif // CRYPTO_IN_SWIFTPM && !CRYPTO_IN_SWIFTPM_FORCE_BUILD_API