.. index:: single: x25519 .. _x25519/0:

.. rst-class:: right

category

x25519

X25519 Diffie-Hellman key agreement implementation (RFC 7748). Requires exact, unbounded integer arithmetic for arithmetic modulo the 255-bit field prime.

| Availability: | logtalk_load(crypto(loader))

| Author: Paulo Moura | Version: 1:0:0 | Date: 2026-08-03

| Compilation flags: | static

| Complements: | :ref:`crypto <crypto/0>` | Uses: | :ref:`list <list/0>` | :ref:`type <type/0>`

| Remarks: | (none)

| Inherited public predicates: | (none)

.. contents:: :local: :backlinks: top

Public predicates

.. index:: x25519_keypair/2 .. _x25519/0::x25519_keypair/2:

x25519_keypair/2 ^^^^^^^^^^^^^^^^^^^^

Generates a fresh random 32-byte PrivateKey and derives the corresponding 32-byte PublicKey. Available only on backends with unbounded integer arithmetic.

| Compilation flags: | static

| Template: | x25519_keypair(PrivateKey,PublicKey) | Mode and number of proofs: | x25519_keypair(-list(byte),-list(byte)) - one

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.. index:: x25519_public_key/2 .. _x25519/0::x25519_public_key/2:

x25519_public_key/2 ^^^^^^^^^^^^^^^^^^^^^^^

Derives the 32-byte X25519 PublicKey corresponding to a 32-byte PrivateKey. Available only on backends with unbounded integer arithmetic.

| Compilation flags: | static

| Template: | x25519_public_key(PrivateKey,PublicKey) | Mode and number of proofs: | x25519_public_key(+list(byte),-list(byte)) - one_or_error

| Exceptions: | PrivateKey is a partial list or a list with an element which is a variable: | instantiation_error | PrivateKey is neither a variable nor a list of 32 bytes: | type_error(list(byte,32),PrivateKey) | PrivateKey contains a non-integer byte: | type_error(integer,Byte) | PrivateKey contains an integer outside the byte range: | domain_error(byte,Byte)

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.. index:: x25519_shared_secret/3 .. _x25519/0::x25519_shared_secret/3:

x25519_shared_secret/3 ^^^^^^^^^^^^^^^^^^^^^^^^^^

Computes the 32-byte X25519 SharedSecret using PrivateKey and PeerPublicKey. Fails when the result is all zeroes. Available only on backends with unbounded integer arithmetic.

| Compilation flags: | static

| Template: | x25519_shared_secret(PrivateKey,PeerPublicKey,SharedSecret) | Mode and number of proofs: | x25519_shared_secret(+list(byte),+list(byte),-list(byte)) - zero_or_one_or_error

| Exceptions: | PrivateKey is a partial list or a list with an element which is a variable: | instantiation_error | PrivateKey is neither a variable nor a list of 32 bytes: | type_error(list(byte,32),PrivateKey) | PrivateKey contains a non-integer byte: | type_error(integer,Byte) | PrivateKey contains an integer outside the byte range: | domain_error(byte,Byte) | PeerPublicKey is a partial list or a list with an element which is a variable: | instantiation_error | PeerPublicKey is neither a variable nor a list of 32 bytes: | type_error(list(byte,32),PeerPublicKey) | PeerPublicKey contains a non-integer byte: | type_error(integer,Byte) | PeerPublicKey contains an integer outside the byte range: | domain_error(byte,Byte)

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Protected predicates

(no local declarations; see entity ancestors if any)

Private predicates

(no local declarations; see entity ancestors if any)

Operators

(none)