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SoftHSM exposes its supported mechanism list through C_GetMechanismList and C_GetMechanismInfo. The list is assembled at startup from prepareSupportedMechanisms() and can be further filtered by the slots.mechanisms configuration option.
Mechanisms that depend on optional compile-time features (ECC, EdDSA, GOST, ML-DSA) are only present when SoftHSM was built with the corresponding flag. FIPS mode disables MD5 and single-DES throughout.

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RSA

MechanismDescription
CKM_RSA_PKCS_KEY_PAIR_GENGenerate an RSA key pair. Supported key sizes: 512 – 16384 bits (in practice, use 2048 or larger).
MechanismDescription
CKM_RSA_PKCSRSA encryption/decryption with PKCS#1 v1.5 padding. Also used for raw sign/verify.
CKM_RSA_X_509Raw RSA (no padding). The caller is responsible for applying padding before calling C_Encrypt.
CKM_RSA_PKCS_OAEPRSA OAEP encryption/decryption. Requires a CK_RSA_PKCS_OAEP_PARAMS parameter specifying the hash and MGF algorithm.
MechanismDescription
CKM_SHA1_RSA_PKCSSHA-1 hash then RSA-PKCS#1 v1.5 signature.
CKM_SHA224_RSA_PKCSSHA-224 hash then RSA-PKCS#1 v1.5 signature.
CKM_SHA256_RSA_PKCSSHA-256 hash then RSA-PKCS#1 v1.5 signature.
CKM_SHA384_RSA_PKCSSHA-384 hash then RSA-PKCS#1 v1.5 signature.
CKM_SHA512_RSA_PKCSSHA-512 hash then RSA-PKCS#1 v1.5 signature.
CKM_MD5_RSA_PKCSMD5 hash then RSA-PKCS#1 v1.5 signature. Disabled in FIPS mode.
CKM_RSA_PKCS_PSSRSA-PSS raw sign/verify (caller pre-hashes). Enabled when built with WITH_RAW_PSS.
CKM_SHA1_RSA_PKCS_PSSSHA-1 hash then RSA-PSS signature.
CKM_SHA224_RSA_PKCS_PSSSHA-224 hash then RSA-PSS signature.
CKM_SHA256_RSA_PKCS_PSSSHA-256 hash then RSA-PSS signature.
CKM_SHA384_RSA_PKCS_PSSSHA-384 hash then RSA-PSS signature.
CKM_SHA512_RSA_PKCS_PSSSHA-512 hash then RSA-PSS signature.
MechanismDescription
CKM_RSA_AES_KEY_WRAPWrap an AES key under an RSA public key using RSA-OAEP + AES-KeyWrap (RFC 5649). Added in SoftHSM 2.7.0. Requires CK_RSA_AES_KEY_WRAP_PARAMS.

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DSA

MechanismDescription
CKM_DSA_PARAMETER_GENGenerate DSA domain parameters (p, q, g).
CKM_DSA_KEY_PAIR_GENGenerate a DSA key pair from previously generated parameters.
MechanismDescription
CKM_DSARaw DSA sign/verify (caller supplies the pre-hashed digest).
CKM_DSA_SHA1SHA-1 hash then DSA signature.
CKM_DSA_SHA224SHA-224 hash then DSA signature.
CKM_DSA_SHA256SHA-256 hash then DSA signature.
CKM_DSA_SHA384SHA-384 hash then DSA signature.
CKM_DSA_SHA512SHA-512 hash then DSA signature.

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Elliptic curve (ECDSA / ECDH)

EC mechanisms are available when SoftHSM is built with --enable-ecc (OpenSSL backend) or the equivalent Botan option. Supported curves include the NIST P-curves (P-256, P-384, P-521) and others provided by the underlying crypto library.
MechanismDescription
CKM_EC_KEY_PAIR_GENGenerate an EC key pair. The curve is specified via the CKA_EC_PARAMS attribute on the public key template (DER-encoded OID).
MechanismDescription
CKM_ECDSARaw ECDSA sign/verify (caller supplies pre-hashed digest).
CKM_ECDSA_SHA1SHA-1 hash then ECDSA signature. Added in SoftHSM 2.7.0.
CKM_ECDSA_SHA224SHA-224 hash then ECDSA signature. Added in SoftHSM 2.7.0.
CKM_ECDSA_SHA256SHA-256 hash then ECDSA signature. Added in SoftHSM 2.7.0.
CKM_ECDSA_SHA384SHA-384 hash then ECDSA signature. Added in SoftHSM 2.7.0.
CKM_ECDSA_SHA512SHA-512 hash then ECDSA signature. Added in SoftHSM 2.7.0.
MechanismDescription
CKM_ECDH1_DERIVEOne-pass ECDH key derivation (requires CK_ECDH1_DERIVE_PARAMS). Available when built with WITH_ECC or WITH_EDDSA.

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EdDSA (Edwards-curve)

EdDSA mechanisms require --enable-eddsa at build time (OpenSSL 1.1.1+ or Botan 2). Ed25519 and Ed448 are supported.
MechanismDescription
CKM_EC_EDWARDS_KEY_PAIR_GENGenerate an Edwards-curve key pair. Specify Ed25519 or Ed448 via CKA_EC_PARAMS.
MechanismDescription
CKM_EDDSAEdDSA sign/verify. Supports both Ed25519 and Ed448. The algorithm is determined by the key’s curve.

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Diffie-Hellman (DH)

MechanismDescription
CKM_DH_PKCS_PARAMETER_GENGenerate DH domain parameters (prime p, base g).
CKM_DH_PKCS_KEY_PAIR_GENGenerate a DH key pair from existing parameters.
MechanismDescription
CKM_DH_PKCS_DERIVEDerive a shared secret from a DH private key and a peer public value.

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AES

MechanismDescription
CKM_AES_KEY_GENGenerate an AES secret key. Key length (16, 24, or 32 bytes) is set via CKA_VALUE_LEN.
MechanismDescription
CKM_AES_ECBAES in Electronic Codebook mode. No IV; not recommended for most use cases.
CKM_AES_CBCAES in Cipher Block Chaining mode. Requires a 16-byte IV.
CKM_AES_CBC_PADAES-CBC with PKCS#7 padding. Handles arbitrary-length plaintext.
CKM_AES_CTRAES in Counter mode. Requires CK_AES_CTR_PARAMS specifying the counter block.
CKM_AES_GCMAES in Galois/Counter mode (authenticated encryption). Requires CK_GCM_PARAMS. Added in SoftHSM 2.4.0.
MechanismDescription
CKM_AES_KEY_WRAPRFC 3394 AES Key Wrap. Wraps keys whose length is a multiple of 8 bytes.
CKM_AES_KEY_WRAP_PADRFC 5649 AES Key Wrap with Padding. Wraps keys of any length. Available when built with HAVE_AES_KEY_WRAP_PAD.
CKM_AES_CBCAES-CBC can also be used for key wrapping (added in SoftHSM 2.6.0).
CKM_AES_CBC_PADAES-CBC with PKCS#7 padding for key wrapping (added in SoftHSM 2.7.0).
MechanismDescription
CKM_AES_ECB_ENCRYPT_DATADerive a key by encrypting a data block with AES-ECB.
CKM_AES_CBC_ENCRYPT_DATADerive a key by encrypting a data block with AES-CBC.
CKM_AES_CMACAES Cipher-based MAC (CMAC / OMAC1). Added in SoftHSM 2.4.0.

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Triple-DES (3DES)

Single-DES key generation (CKM_DES_KEY_GEN) and single-DES cipher modes (CKM_DES_ECB, CKM_DES_CBC, CKM_DES_CBC_PAD) are disabled in FIPS mode. Triple-DES is available in both standard and FIPS builds.
MechanismDescription
CKM_DES_KEY_GENGenerate a single-DES key (8 bytes). Disabled in FIPS mode.
CKM_DES2_KEY_GENGenerate a two-key Triple-DES key (16 bytes).
CKM_DES3_KEY_GENGenerate a three-key Triple-DES key (24 bytes).
MechanismDescription
CKM_DES_ECBSingle-DES ECB mode. Disabled in FIPS mode.
CKM_DES_CBCSingle-DES CBC mode. Disabled in FIPS mode.
CKM_DES_CBC_PADSingle-DES CBC with PKCS#7 padding. Disabled in FIPS mode.
CKM_DES3_ECBTriple-DES ECB mode.
CKM_DES3_CBCTriple-DES CBC mode.
CKM_DES3_CBC_PADTriple-DES CBC with PKCS#7 padding. Wrapping also supported (added in SoftHSM 2.7.0).
MechanismDescription
CKM_DES_ECB_ENCRYPT_DATADerive a key by encrypting data with single-DES ECB. Disabled in FIPS mode.
CKM_DES_CBC_ENCRYPT_DATADerive a key by encrypting data with single-DES CBC. Disabled in FIPS mode.
CKM_DES3_ECB_ENCRYPT_DATADerive a key by encrypting data with Triple-DES ECB.
CKM_DES3_CBC_ENCRYPT_DATADerive a key by encrypting data with Triple-DES CBC.
CKM_DES3_CMACTriple-DES Cipher-based MAC. Added in SoftHSM 2.4.0.

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Hash (digest)

MechanismOutput lengthNotes
CKM_MD516 bytesDisabled in FIPS mode
CKM_SHA_120 bytes
CKM_SHA22428 bytes
CKM_SHA25632 bytes
CKM_SHA38448 bytes
CKM_SHA51264 bytes
Digest operations are performed with C_DigestInit / C_Digest (single-part) or C_DigestInit / C_DigestUpdate / C_DigestFinal (multi-part).

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HMAC

MechanismUnderlying hashOutput lengthNotes
CKM_MD5_HMACMD516 bytesDisabled in FIPS mode
CKM_SHA_1_HMACSHA-120 bytes
CKM_SHA224_HMACSHA-22428 bytes
CKM_SHA256_HMACSHA-25632 bytes
CKM_SHA384_HMACSHA-38448 bytes
CKM_SHA512_HMACSHA-51264 bytes
Per PKCS#11 3.0, the minimum HMAC key size is equal to the hash output length. SoftHSM enforces this lower bound when initializing an HMAC operation.

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GOST

GOST mechanisms require --enable-gost at build time. This is a compile-time optional feature and is not available in standard binary packages.
MechanismDescription
CKM_GOSTR3410_KEY_PAIR_GENGenerate a GOST R 34.10-2001 key pair
CKM_GOSTR3410GOST R 34.10-2001 raw sign/verify
CKM_GOSTR3410_WITH_GOSTR3411GOST R 34.10-2001 with GOST R 34.11-94 hash
CKM_GOSTR3411GOST R 34.11-94 (Streebog) hash
CKM_GOSTR3411_HMACHMAC using GOST R 34.11-94

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ML-DSA (Module-Lattice Digital Signature Algorithm)

ML-DSA is a post-quantum lattice-based signature algorithm (formerly known as CRYSTALS-Dilithium, standardized as FIPS 204). These mechanisms require SoftHSM to be built against OpenSSL 3.x with ML-DSA support enabled (WITH_ML_DSA).
MechanismDescription
CKM_ML_DSA_KEY_PAIR_GENGenerate an ML-DSA key pair. The parameter set (ML-DSA-44, ML-DSA-65, ML-DSA-87) is selected via the key template.
CKM_ML_DSAML-DSA sign/verify.

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Generic secret key generation

MechanismDescription
CKM_GENERIC_SECRET_KEY_GENGenerate a generic secret key of arbitrary length for use as HMAC or derivation base keys.

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Key derivation utilities

These mechanisms are used as part of derived key construction and are available unconditionally.
MechanismDescription
CKM_CONCATENATE_DATA_AND_BASEDerive a key by prepending data to a base key value.
CKM_CONCATENATE_BASE_AND_DATADerive a key by appending data to a base key value.
CKM_CONCATENATE_BASE_AND_KEYDerive a key by concatenating two key values.

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Random number generation

SoftHSM uses the RNG provided by the underlying cryptographic library (OpenSSL or Botan). Applications interact with it through the standard PKCS#11 functions:
FunctionDescription
C_GenerateRandomFill a buffer with cryptographically random bytes
C_SeedRandomMix additional entropy into the RNG state
There is no separate CKM_ constant for RNG; random generation is invoked directly via these functions rather than through the mechanism API.

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Mechanism availability by build configuration

Build flagMechanisms enabled
(always on)RSA, DSA, DH, 3DES, AES, SHA-1/224/256/384/512, HMAC, generic secret
WITH_FIPS disabledMD5, CKM_MD5_HMAC, CKM_MD5_RSA_PKCS, single-DES
WITH_ECCCKM_EC_KEY_PAIR_GEN, CKM_ECDSA*, CKM_ECDH1_DERIVE
WITH_EDDSACKM_EC_EDWARDS_KEY_PAIR_GEN, CKM_EDDSA, CKM_ECDH1_DERIVE
WITH_GOSTCKM_GOSTR3410*, CKM_GOSTR3411*
WITH_ML_DSACKM_ML_DSA_KEY_PAIR_GEN, CKM_ML_DSA
WITH_RAW_PSSCKM_RSA_PKCS_PSS (raw, pre-hashed)
HAVE_AES_KEY_WRAP_PADCKM_AES_KEY_WRAP_PAD
To restrict which mechanisms are active at runtime without recompiling, set slots.mechanisms in softhsm2.conf to a comma-separated list of mechanism names (e.g., CKM_AES_GCM,CKM_SHA256_RSA_PKCS). The default value ALL enables every compiled-in mechanism.

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