package mirage-crypto

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The ChaCha20 cipher proposed by D.J. Bernstein.

include AEAD
val tag_size : int

The size of the authentication tag.

type key

The abstract type for the key.

val of_secret : Cstruct.t -> key

of_secret secret constructs the encryption key corresponding to secret.

Authenticated encryption and decryption with inline tag

val authenticate_encrypt : key:key -> nonce:Cstruct.t -> ?adata:Cstruct.t -> Cstruct.t -> Cstruct.t

authenticate_encrypt ~key ~nonce ~adata msg encrypts msg with key and nonce, and appends an authentication tag computed over the encrypted msg, using key, nonce, and adata.

val authenticate_decrypt : key:key -> nonce:Cstruct.t -> ?adata:Cstruct.t -> Cstruct.t -> Cstruct.t option

authenticate_decrypt ~key ~nonce ~adata msg splits msg into encrypted data and authentication tag, computes the authentication tag using key, nonce, and adata, and decrypts the encrypted data. If the authentication tags match, the decrypted data is returned.

Authenticated encryption and decryption with tag provided separately

val authenticate_encrypt_tag : key:key -> nonce:Cstruct.t -> ?adata:Cstruct.t -> Cstruct.t -> Cstruct.t * Cstruct.t

authenticate_encrypt_tag ~key ~nonce ~adata msg encrypts msg with key and nonce. The computed authentication tag is returned separately as second part of the tuple.

val authenticate_decrypt_tag : key:key -> nonce:Cstruct.t -> ?adata:Cstruct.t -> tag:Cstruct.t -> Cstruct.t -> Cstruct.t option

authenticate_decrypt ~key ~nonce ~adata ~tag msg computes the authentication tag using key, nonce, and adata, and decrypts the encrypted data. If the authentication tags match, the decrypted data is returned.

val crypt : key:key -> nonce:Cstruct.t -> ?ctr:int64 -> Cstruct.t -> Cstruct.t

crypt ~key ~nonce ~ctr data generates a ChaCha20 key stream using the key, and nonce. The ctr defaults to 0. The generated key stream is of the same length as data, and the output is the XOR of the key stream and data. This implements, depending on the size of the nonce (8 or 12 bytes) both the original specification (where the counter is 8 byte, same as the nonce) and the IETF RFC 8439 specification (where nonce is 12 bytes, and counter 4 bytes).

  • raises Invalid_argument

    if invalid parameters are provided. Valid parameters are: key must be 32 bytes and nonce 12 bytes for the IETF mode (and counter fit into 32 bits), or key must be either 16 bytes or 32 bytes and nonce 8 bytes.