Technology

SSH Key Algorithms

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Source:Community curated
Updated:4/9/2026
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Algorithm
Type
Typical Size
Year Standardized
Status in 2026
Known For
Ed25519
EdDSA on Curve25519256-bit2011RecommendedModern default, tiny keys, fast, resistant to side-channel and bad RNG, designed by Daniel J. Bernstein
RSA 4096
RSA4096-bit1977Safe but largeClassic choice, slow signing, 4096-bit used as conservative default in corporate environments
RSA 3072
RSA3072-bit1977AcceptableNIST-equivalent of 128-bit symmetric security, sweet spot for RSA compatibility
RSA 2048
RSA2048-bit1977Minimum acceptableStill ubiquitous, fine until ~2030, smallest safely-used RSA size
RSA 1024
RSA1024-bit1977DeprecatedConsidered broken, rejected by modern OpenSSH defaults, still lurking in legacy systems
ECDSA P-256
ECDSA on NIST P-256256-bit2000AcceptableFast, small keys, but vulnerable to bad nonces (see Sony PS3), NIST curve trust issues
ECDSA P-384
ECDSA on NIST P-384384-bit2000AcceptableConservative ECDSA option, required by some US government profiles, slower than P-256
ECDSA P-521
ECDSA on NIST P-521521-bit2000Rarely usedHighest-strength ECDSA in common use, overkill for most workloads
DSA 1024
DSA1024-bit1994Disabled by defaultRemoved as an OpenSSH default in 7.0 (2015), fixed-size, considered obsolete
Ed448
EdDSA on Curve448456-bit2017EmergingHigher security margin than Ed25519, slower, rarely used but present in modern OpenSSH
sk-ecdsa-sha2-nistp256 (FIDO)
ECDSA + hardware token256-bit2020Recommended for hardwareHardware-backed ECDSA tied to YubiKey/FIDO2, requires touch to sign
sk-ssh-ed25519 (FIDO)
Ed25519 + hardware token256-bit2020Recommended for hardwareHardware-backed Ed25519, strongest practical SSH key, YubiKey 5+ support
RSA 8192
RSA8192-bit1977ParanoidUsed by tinfoil hats, painfully slow, little real-world advantage over RSA 4096
ssh-rsa (SHA-1)
RSA + SHA-1 signingVariable1995Disabled in OpenSSH 8.8Old default signature type, disabled in OpenSSH 8.8 (2021) due to SHA-1 weakness
Ed25519-SK (resident)
Ed25519 resident key256-bit2021EmergingResident key stored on FIDO2 device, portable across machines with just the token

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