Configure invalid RSA public key size: registry value invalidrsabitsUserHKCU\software\policies\microsoft\office\16.0\common\signatures

Policy ID: L_SelectDigitalSignatureInvalidRSABits
Scope: User Configuration
Supported on: At least Windows Server 2008 R2 or Windows 7
Source: Microsoft 365 Apps / Office Administrative Templates (version 5568.1000)
Category: Microsoft Office 2016 › Security Settings › Digital Signatures

Registry

invalidrsabits

REG_DWORDUser

HKCU\software\policies\microsoft\office\16.0\common\signatures Current key

Enabled value: Depends on the option value
Element: -

Options
Item	Stored value
0	0
512	512
768	768
1024	1024
1536	1536
2048	2048

Apply with .reg · CMD · PowerShell

.reg

Windows Registry Editor Version 5.00

[HKEY_CURRENT_USER\software\policies\microsoft\office\16.0\common\signatures]

; Options (use only one)
; 0
"invalidrsabits"=dword:00000000
; 512
"invalidrsabits"=dword:00000200
; 768
"invalidrsabits"=dword:00000300
; 1024
"invalidrsabits"=dword:00000400
; 1536
"invalidrsabits"=dword:00000600
; 2048
"invalidrsabits"=dword:00000800

CMD

:: Options (use only one)

:: 0
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 0 /f
:: 512
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 512 /f
:: 768
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 768 /f
:: 1024
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 1024 /f
:: 1536
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 1536 /f
:: 2048
reg add "HKCU\software\policies\microsoft\office\16.0\common\signatures" /v "invalidrsabits" /t REG_DWORD /d 2048 /f

PowerShell

# Common: create the key
New-Item -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Force | Out-Null

# Options (use only one)
# 0
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 0 -Force | Out-Null
# 512
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 512 -Force | Out-Null
# 768
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 768 -Force | Out-Null
# 1024
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 1024 -Force | Out-Null
# 1536
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 1536 -Force | Out-Null
# 2048
New-ItemProperty -Path 'HKCU:\software\policies\microsoft\office\16.0\common\signatures' -Name 'invalidrsabits' -PropertyType DWord -Value 2048 -Force | Out-Null