[#CRYPTO_nistcts128_decrypt]
= CRYPTO_nistcts128_decrypt
:mrdocs:

Decrypt NIST CS2/CS3‐style ciphertext stealing using a CBC decrypt function.

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
size_t
CRYPTO_nistcts128_decrypt(
    unsigned char const* in,
    unsigned char* out,
    size_t len,
    void const* key,
    unsigned char ivec[],
    xref:cbc128_f.adoc[cbc128_f] cbc);
----

== Return Value

Number of plaintext bytes written, or 0 on error.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *in*
| Input ciphertext of length `len` (must be at least 16).
| *out*
| Output plaintext buffer of length `len.`
| *len*
| Number of ciphertext bytes.
| *key*
| Cipher‐specific expanded key for `cbc.`
| *ivec*
| 16‐byte IV updated like CBC.
| *cbc*
| CBC‐mode decrypt function for the underlying cipher.
|===


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