OPENSSL_S390XCAP(3ossl)

📦
version 3.5.9 · 8 versions
, in fedora 43, fedora 44

💖 OPENSSL_S390XCAP 💖

okay bestie, welcome to OPENSSL_s390xcap(3ossl) — the page that explains the IBM z processor capabilities vector. yes it's a whole vibe. yes it's real. let's go 🦋

✨ NAME ✨

OPENSSL_s390xcap — the IBM z processor capabilities vector 💅

✨ SYNOPSIS ✨

env OPENSSL_s390xcap=... <application>

✨ DESCRIPTION ✨

okay so here's the tea 🍓: libcrypto supports z/Architecture instruction set extensions. Each of those extensions gets its own lil bit in the capabilities vector. When libcrypto initializes, the bits that come back from the STFLE instruction and from the QUERY functions get stored in that vector. iconic behavior honestly.

so if you wanna change which instructions your app can actually use, you set the OPENSSL_s390xcap environment variable before you start the app. after initialization, the capability vector gets ANDed bitwise with a mask that's derived from that environment variable. cute, right?

the environment variable is a semicolon-separated list of tokens, and it gets processed left to right (whitespace is ignored, she's chill):

OPENSSL_s390xcap="<tok1>;<tok2>;..."

there are four types of tokens, and we're gonna go through every single one because I would never gatekeep 👑

🎀 the token types 🎀

  • <string> — the name of a processor generation. a bit in the environment variable's mask is set to one if and only if the specified processor generation implements the corresponding instruction set extension. possible values are z900, z990, z9, z10, z196, zEC12, z13, z14, z15, and z16. that's the whole roster bestie 💜
  • <string>:<mask>:<mask> — the name of an instruction followed by two 64-bit masks. the part of the environment variable's mask corresponding to that specified instruction is set to the specified 128-bit mask. possible values are kimd, klmd, km, kmc, kmac, kmctr, kmo, kmf, prno, kma, pcc and kdsa. yes that's a lot of k-words, we love a theme 🌸
  • stfle:<mask>:<mask>:<mask> — store-facility-list-extended (stfle) followed by three 64-bit masks. the part of the environment variable's mask corresponding to the stfle instruction is set to the specified 192-bit mask. three masks, one girl 🫶
  • nocex — deactivate modular exponentiation and CRT operation offloading to Crypto Express Adapters. bye bye offload 💀

the 64-bit masks are written in hexadecimal notation. the 0x prefix is optional (she's flexible like that). and if you prefix a mask with a tilde, ~, that denotes a bitwise NOT operation. noted 📝

🔥 the significant bits, per instruction 🔥

here's the list of significant bits for each instruction. colon rows separate the individual 64-bit masks. the bit numbers in the first column are consistent with [1] — meaning 0 denotes the leftmost bit and the numbering is continuous across 64-bit mask boundaries. so the three columns you're looking at are Bit, Mask, and Facility/Function. don't let the layout jump you, it's just three columns ✨

⭐ stfle

     # 17    1<<46    message-security assist
     # 25    1<<38    store-clock-fast facility
     :
     # 76    1<<51    message-security assist extension 3
     # 77    1<<50    message-security assist extension 4
     # 86    1<<41    message-security-assist extension 12
     :
     #129    1<<62    vector facility
     #134    1<<57    vector packed decimal facility
     #135    1<<56    vector enhancements facility 1
     #146    1<<45    message-security assist extension 8
     #155    1<<36    message-security assist extension 9

⭐ kimd

     #  1    1<<62    KIMD-SHA-1
     #  2    1<<61    KIMD-SHA-256
     #  3    1<<60    KIMD-SHA-512
     # 32    1<<31    KIMD-SHA3-224
     # 33    1<<30    KIMD-SHA3-256
     # 34    1<<29    KIMD-SHA3-384
     # 35    1<<28    KIMD-SHA3-512
     # 36    1<<27    KIMD-SHAKE-128
     # 37    1<<26    KIMD-SHAKE-256
     :
     # 65    1<<62    KIMD-GHASH

⭐ klmd

     # 32    1<<31    KLMD-SHA3-224
     # 33    1<<30    KLMD-SHA3-256
     # 34    1<<29    KLMD-SHA3-384
     # 35    1<<28    KLMD-SHA3-512
     # 36    1<<27    KLMD-SHAKE-128
     # 37    1<<26    KLMD-SHAKE-256
     :

⭐ km

     # 18    1<<45    KM-AES-128
     # 19    1<<44    KM-AES-192
     # 20    1<<43    KM-AES-256
     # 50    1<<13    KM-XTS-AES-128
     # 52    1<<11    KM-XTS-AES-256
     :
     # 82    1<<45    KM-XTS-AES-128-MSA10
     # 84    1<<43    KM-XTS-AES-256-MSA10

⭐ kmc

     # 18    1<<45    KMC-AES-128
     # 19    1<<44    KMC-AES-192
     # 20    1<<43    KMC-AES-256
     :

⭐ kmac

     # 18    1<<45    KMAC-AES-128
     # 19    1<<44    KMAC-AES-192
     # 20    1<<43    KMAC-AES-256
     :
     # 112   1<<15    KMAC-SHA-224
     # 113   1<<14    KMAC-SHA-256
     # 114   1<<13    KMAC-SHA-384
     # 115   1<<12    KMAC-SHA-512

⭐ kmctr

     :

(that lone colon is doing so much emotional labor 😭 it's just the 64-bit mask separator, nothing else here)

⭐ kmo

     # 18    1<<45    KMO-AES-128
     # 19    1<<44    KMO-AES-192
     # 20    1<<43    KMO-AES-256
     :

⭐ kmf

     # 18    1<<45    KMF-AES-128
     # 19    1<<44    KMF-AES-192
     # 20    1<<43    KMF-AES-256
     :

⭐ prno

     :

(again — just the separator, bestie 🙈)

⭐ kma

     # 18    1<<45    KMA-GCM-AES-128
     # 19    1<<44    KMA-GCM-AES-192
     # 20    1<<43    KMA-GCM-AES-256
     :

⭐ pcc

     :
     # 64    1<<63    PCC-Scalar-Multiply-P256
     # 65    1<<62    PCC-Scalar-Multiply-P384
     # 66    1<<61    PCC-Scalar-Multiply-P521
     # 72    1<<55    PCC-Scalar-Multiply-Ed25519
     # 73    1<<54    PCC-Scalar-Multiply-Ed448
     # 80    1<<47    PCC-Scalar-Multiply-X25519
     # 81    1<<46    PCC-Scalar-Multiply-X448

⭐ kdsa

     #  1    1<<62    KDSA-ECDSA-Verify-P256
     #  2    1<<61    KDSA-ECDSA-Verify-P384
     #  3    1<<60    KDSA-ECDSA-Verify-P521
     #  9    1<<54    KDSA-ECDSA-Sign-P256
     # 10    1<<53    KDSA-ECDSA-Sign-P384
     # 11    1<<52    KDSA-ECDSA-Sign-P521
     # 32    1<<31    KDSA-EdDSA-Verify-Ed25519
     # 36    1<<27    KDSA-EdDSA-Verify-Ed448
     # 40    1<<23    KDSA-EdDSA-Sign-Ed25519
     # 44    1<<19    KDSA-EdDSA-Sign-Ed448
     :

✨ RETURN VALUES ✨

not available. she said no 💅 (there's genuinely nothing to return here, that's the whole answer)

✨ EXAMPLES ✨

🦋 disable everything the z196 doesn't implement

disables all instruction set extensions which the z196 processor does not implement:

OPENSSL_s390xcap="z196"

🦋 disable the vector facility

disables the vector facility:

OPENSSL_s390xcap="stfle:~0:~0:~0x4000000000000000"

🦋 disable specific function codes

disables the KM-XTS-AES and the KIMD-SHAKE function codes:

OPENSSL_s390xcap="km:~0x2800:~0;kimd:~0xc000000:~0"

✨ SEE ALSO ✨

  • [1] z/Architecture Principles of Operation, SA22-7832-12

Copyright 2018-2024 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at <https://www.openssl.org/source/license.html>.

and that's the page bestie 🫶 this was OPENSSL_S390XCAP(3ossl), version 3.5.9, dated 2026-09-29 — go forth and mask your bits, you absolute icon 👑✨

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