[#CRYPTO_ctr128_encrypt]
= CRYPTO_ctr128_encrypt
:mrdocs:

Encrypt or decrypt with a 128‐bit block cipher in CTR mode.

== Synopsis

Declared in `<openssl/modes.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
void
CRYPTO_ctr128_encrypt(
    unsigned char const* in,
    unsigned char* out,
    size_t len,
    void const* key,
    unsigned char ivec[],
    unsigned char ecount_buf[],
    unsigned int* num,
    xref:block128_f.adoc[block128_f] block);
----

== Parameters

[cols="1,4"]
|===
| Name| Description
| *in*
| Input bytes of length `len.`
| *out*
| Output buffer of length `len` (may equal `in).`
| *len*
| Number of bytes to process.
| *key*
| Cipher‐specific expanded key for `block.`
| *ivec*
| 16‐byte counter block updated as encryption proceeds.
| *ecount_buf*
| 16‐byte buffer holding the current encrypted counter block.
| *num*
| Offset into `ecount_buf` for residual keystream (updated; start at 0).
| *block*
| Block‐encrypt function for the underlying cipher.
|===


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