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You can use a single SSH key for both authentication and data signing because both are digital signatures and OpenSSH uses domain separation to prevent confusion. Use separate keys when you need longer-term signing keys (e.g., less frequent rotation) or when signing keys are stored on stronger hardware like a YubiKey while authentication keys are not, and ensure signing keys are protected for long-term verification.
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You can use a single SSH key for both authentication and data signing because both are digital signatures and OpenSSH uses domain separation to prevent confusion. Use separate keys when you need longer-term signing keys (e.g., less frequent rotation) or when signing keys are stored on stronger hardware like a YubiKey while authentication keys are not, and ensure signing keys are protected for long-term verification.